Category 6™

Landmark climate change report coming Friday

By: JeffMasters, 3:46 PM GMT on January 31, 2007

Every six years, the United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC) releases a massive and influential study detailing the state of Earth's climate. This Friday marks the release of the first IPCC report since 2001. To help preview this blockbuster study, I've asked climate expert Dr. Richard Rood to help out. Dr. Rood is a climate modeler and professor of Meteorology at the University of Michigan, and has authored nearly 100 scientific papers on climate change and meteorology. After today's guest appearance on my blog, Dr. Rood will be contributing a series of blogs on climate change that will appear in a new featured "Climate Change" blog. Take it away, ricky!

What is the IPCC?

On February 2, 2007 the Intergovernmental Panel on Climate Change (IPCC) is scheduled to release the first of a series of reports that describe the current state of the Earth's climate, how it has changed, and how it is expected to change in the future. "Climate Change 2007" will be definitive and influential. Climate change touches every aspect of society, and there is already controversy associated with the release. This is the first of a series of blogs about climate and climate change; it discusses the process of development of these official assessments.

First, the IPCC is not a research organization, but relies upon research performed and reported by scientists from all over the world. This underlying research is based on observations and the development of testable propositions to determine cause and effect in the behavior of the observations. Sometimes the propositions can be tested with experiments, but more often climate scientists use models to predict the behavior of the observations. Therefore, like weather forecasting, the success or failure of model predictions reveal our level of understanding.

Part of the scientific process is the ability of independent researchers to investigate the observations and extract information. If their conclusions converge, then the independent nature of the investigations adds accountability to the process. That is, there are checks and balances which constantly challenge, check, and re-check the conclusions of individual scientists. The IPCC assesses this body of scientific literature; it is not just the research of the United States; it is the research of the world. It is research hardened by the competition of ideas and honed by the survival of the successful ideas.

The scientists who write the IPCC reports use exquisite rigor. The reports are written by experts drawn from around the world, selected to assure the representation of the members of the United Nations. Draft reports are then reviewed by experts who were not authors of the report. Then there is review by government officials involved in policy making. All told, there are more than 1000 contributing authors, and more than 2000 independent reviewers. All comments are considered in the revisions that lead to the production of the final document. The time commitment is enormous, and the result is a document which is based on the facts of observation and predictions which have been scrutinized to the highest level possible.

The Intergovernmental Panel on Climate Change is sponsored by the World Meteorological Organization and the United Nations Environment Program. Their home page is at


Climate Change

Spectacular cloud holes yesterday

By: JeffMasters, 5:01 PM GMT on January 30, 2007

An unusually large series of cloud holes developed over Mississippi, Louisiana, Texas, Arkansas, and Alabama yesterday, which were captured by several alert wunderphotographers (see the thumbnail images at the bottom). These cloud holes (also called "dissipation trails" or "distrails") are formed when an aircraft passes through a deck of clouds containing water drops that have cooled below the freezing point of water. The exhaust particles of the aircraft's engines serve as nuclei for the supercooled water drops to freeze on, and the resulting ice crystals fall towards the ground as "fall streaks". Also, engine heat and turbulence along the wing tips mixes moist and dry air, helping create clear holes. It typically takes about 20 minutes for a cloud hole to form after an airplane has passed, so it is not obvious that a aircraft create the holes.

Visible image of the clouds holes of January 29, 2007, as seen by NASA's Terra satellite.

For more detailed information on this event, including animations and upper-air plots, see the University of Wisconsin CIMSS Satellite blog.

I'll have a preview on Wednesday of the upcoming blockbuster climate report scheduled to be released Friday by the U.N. Intergovernmental Panel on Climate Change (IPCC).

Jeff Masters

Atmospheric Phenomena

Nuclear war and climate change

By: JeffMasters, 5:31 AM GMT on January 29, 2007

In the 1980s and early 1990s, a series of scientific papers published by Soviet scientists and Western scientists (including "rock star" scientists Dr. Carl Sagan, host of the PBS "Cosmos" TV series, and Nobel Prize winner Paul Crutzen) laid out the dire consequences on global climate of a major nuclear exchange between the U.S. and Soviet Union. The nuclear explosions would send massive clouds of dust high into the stratosphere, blocking so much sunlight that a nuclear winter would result. Global temperatures would plunge 20°C to 40°C for several months, and remain 2-6°C lower for 1-3 years. Up to 70% of the Earth's protective stratospheric ozone layer would be destroyed, allowing huge doses of ultraviolet light to reach the surface. This UV light would kill much of the marine life that forms the basis of the food chain, resulting in the collapse many fisheries and the starvation of the people and animals that depend it. The UV light would also blind huge numbers of animals, who would then wander sightlessly and starve. The cold and dust would create widespread crop failures and global famine, killing billions of people who did not die in the nuclear explosions.

What about a small-scale nuclear war?
The "nuclear winter" papers were widely credited with helping lead to the nuclear arms reduction treaties of the 1990s, as it was clear that we risked catastrophic global climate change in the event of a full-scale nuclear war. But even a limited nuclear war poses a significant threat to Earth's climate, according to a paper presented at the American Geophysical Union meeting in December by scientists at Rutgers University and the University of Colorado. The scientists used a sophisticated atmospheric/oceanic climate model that had a good track record simulating the cooling effects of past major volcanic eruptions, such as the Philippines' Mt. Pinatubo in 1991. The scientists injected five terragrams of soot particles into the model atmosphere over Pakistan in May of 2006. This amount of smoke, they argued, would be the likely result of a limited nuclear war involving 100 Hiroshima-sized bombs in the region.

Figure 1. Global average temperature departure from normal since 1880 (top) and A.D. 1000 (bottom) in black, and those projected after a limited nuclear exchange of 100 Hiroshima-sized weapons in 2006 (in red). Temperatures are forecast to plunge 1.2°C (2.2°F) after such a war, reaching levels colder than anything seen in the past 1000 years. The 1815 eruption of Tambora in Indonesia produced a similar cooling, and led to the notorious "Year Without a Summer". Image credit: "Climatic consequences of a regional nuclear conflict" by Robock et al., 2006.

The black smoke, they found, absorbed far more solar radiation than the brighter sulfuric acid particles emitted by volcanic eruptions. This allowed the smoke to heat the surrounding air to much higher temperatures, resulting in stronger upward motion of the smoke particles higher into the stratosphere. Once the smoke reached the stratosphere, where there is no rain to rain out the soot particles, it stayed at significantly high levels for over a decade. The black soot blocked sunlight, resulting in global cooling of over 1.2°C (2.2°F) for two years, and 0.5°C (0.9°F) for more than a decade.

This magnitude of this cooling would bring about the coldest temperatures observed on the globe in over 1000 years (Figure 1). The growing season would shorten by 10-30 days over much of the globe, resulting in widespread crop failures. The effects would be similar to what happened after the greatest volcanic eruption in historic times, the 1815 Tambora eruption in Indonesia. This cooling from this eruption triggered the infamous Year Without a Summer in 1816 in the Northern Hemisphere, when killing frosts disrupted agriculture every month of the summer in New England, creating terrible hardship. Exceptionally cold and wet weather in Europe triggered widespread harvest failures, resulting in famine and economic collapse. However, the cooling effect of this eruption only lasted about a year. Cooling from a limited nuclear exchange would create two to three consecutive "Years Without a Summer", and over a decade of significantly reduced crop yields. The authors anticipated that the smoke in the stratosphere would partially destroy Earth's protective stratospheric ozone layer as well, but did not model how large of an impact this would have. Clearly, even a limited nuclear exchange could trigger severe global climate change capable of causing economic chaos and widespread starvation.

Climate change and the Doomsday Clock
It is sobering to realize that the nuclear weapons used in the Robock et al. study represented only 0.03% of the world's total nuclear arsenal of 26,000 warheads. While significant progress was made in the 1990s to reduce the threat of nuclear war, that threat has increased in recent years. Last week's move by the Bulletin of the Atomic Scientists to move the hands of their Doomsday Clock two minutes closer to midnight--the figurative end of civilization--helped call attention to this increased threat. In addition, they also mentioned climate change for the first time as part of the rationale for moving the clock closer to midnight. I believe that climate change does not pose an immediate threat to civilization--at least for the next 20 years or so--and there is still time to significantly reduce the threat of climate change to civilization if strong action is taken in the next 20 years to cut carbon emissions. Thus, setting the hands of the clock closer to midnight because of climate change is probably premature. However, climate change triggered by a limited nuclear war is a whole different situation. The twin disasters of a limited nuclear war, coupled with the devastating global climate change it could wreak, should remind us that there is no such thing as a small scale nuclear war. Nuclear war remains the greatest threat to the globe, and the most important cause to work for today is peace. There's no better way for an individual to do that than to make oneself more peaceful.

Next update
On Wednesday, I'll preview the coming blockbuster climate report due to be issued this Friday by the United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC).

Jeff Masters

Winter is back to normal

By: JeffMasters, 2:38 PM GMT on January 26, 2007

Winter is back to normal across most of the Northern Hemisphere this week, as Europe finally got its first major snowstorm and cold air outbreak. A powerful low pressure system swept across Europe this week, causing numerous flight delays and traffic accidents across Germany, France, and Austria. About 5,000 vehicles were stranded in eastern France when the A6 motorway was cut off by snow. Over 200 police and firefighters were sent to help stranded motorists. Over a meter of snow fell in the Alps, bringing ski areas their first decent snows this winter. London got their first significant snow of winter, as well.

Figure 1. The long-range forecast for February, March, and April. Image credit: Columbia University's International Research Institute for Climate and Society.

The 2-week forecast from the GFS model foresees a fairly normal winter pattern for the next two weeks over the Northern Hemisphere. The long-range forecast for the rest of winter and early spring (Figure 1) from Columbia University's International Research Institute for Climate and Society also predicts a fairly normal weather pattern for the coming three months. Most of Europe, North America, and northern Asia are predicted to have near normal to slightly above normal temperatures. Record high temperatures are most likely over portions of Africa, South America, and Southeast Asia.

Jeff Masters

Winter Weather

State of U.S. global warming efforts: Business as Usual

By: JeffMasters, 2:49 PM GMT on January 24, 2007

President Bush spoke of "the serious challenge of global climate change" in his State of the Union speech last night, and called for the U.S. to reduce gasoline consumption 20 percent over the next 10 years. The reduction in gasoline consumption would primarily be achieved through promotion of alternative fuels such as ethanol and liquefied coal. While it is a pleasant change to hear the president acknowledge the reality of the climate change problem and to propose measures that could significantly reduce U.S. consumption of foreign oil, his proposals do virtually nothing to combat global warming.

About one third of greenhouse gases emissions in the the U.S. come from cars and trucks. Thus, a 20% cut in gasoline consumption would reduce U.S. greenhouse gas emissions by about 6%, at best. Since a large portion of the gasoline reduction would come from liquefied coal--which, when burned, makes double the CO2 of burning gasoline--even this modest 6% decrease in emissions might end up at zero. The President offered no plan to reduce greenhouse gas emissions from electric utilities or industry, whose emissions will continue to grow at about 2% per year. Overall, greenhouse gas emission will grow by 14% over the next decade under the President's plan, according to Philip Clapp, president of the National Environmental Trust. The consensus among most climate scientists is that emission of greenhouse gases must be radically cut 50-60% globally by 2050 in order to avoid dangerous levels of global warming. The President's business-as-usual plan to allow emissions to increase by 14% over the next decade will make it extremely difficult to achieve that goal, as the U.S. contributes about 25% of the world's greenhouse gas emissions.

Jeff Masters

Climate Change

Good news for the 2007 hurricane season

By: JeffMasters, 3:09 PM GMT on January 22, 2007

There's plenty of hurricane-related news to report from last week's annual meeting of the American Meteorological Society (AMS) in San Antonio, Texas. The best news is that the Air Force Hurricane Hunter C-130 aircraft are expected to get a major upgrade of their instrumentation for the 2007 season, thanks to $10.5 million in supplemental funding approved by Congress in December 2004. At least four Air Force C-130 aircraft will receive new Stepped Frequency Microwave Radiometer (SFMR) instruments. The first SFMR-equipped Air Force C-130 is scheduled to be on-line in June. The SFMR (or "Smurf") is able to directly measure the wind speed at the ocean surface. The instrument has been flown operationally by NOAA's two P-3 hurricane hunter aircraft since 1999, and has repeatedly provided crucial estimates of the landfall intensity of numerous hurricanes, particularly during the ferocious hurricane seasons of 2004 and 2005. The SFMR works by studying the brightness of the surface at microwave wavelengths. Strong winds kick up sea spray that makes the ocean white with large foam patches. The amount of microwave energy seen by the instrument is proportional to the whiteness of the ocean surface, and therefore the wind speed. This measurement of the surface winds is far more accurate than trying to infer the surface winds from winds measured at flight level. For example, as Hurricane Katrina approached landfall in 2005, the winds measured at flight level (10,000 feet) stayed roughly constant, while the surface winds fell from Category 5 to Category 3 speeds as the hurricane weakened. The SFMR correctly diagnosed Katrina's sudden weakening at landfall, enabling NHC to issue more accurate advisories.

NOAA's two P-3 hurricane hunter aircraft have flown the SFMR instrument since the late 1980's, so we have a lot of calibration data that has greatly increased our confidence in the reliability of these wind measurements. Comparison of SFMR winds with dropsonde and buoy measurements in hurricanes have shown that the SFMR winds are in error by less than 8 mph about 50% of the time. Thus, we can estimate the surface winds in a hurricane to an accuracy of about 10% using the SFMR.

The SFMR instrument requires about 10 seconds to make a measurement. At the typical flight speed of a C-130 or P-3 hurricane hunter aircraft, the winds are effectively averaged over about 1.5 km along the flight track. According to Uhlhorn and Black (2003), the SFMR instrument underestimates the winds in the right-rear quadrant of northern hemisphere storms. This occurs because the wind is aligned with the direction the waves propagate, resulting in building waves that do not produce very large foam patches in their wake after breaking.

Other hurricane news
Another piece of good news this hurricane season--both of NOAA's P-3 aircraft will both be available for hurricane duty. Last year, only one of these aircraft was available. A third P-3 is on order and due to be operational by 2009, but the latest budget has no money to crew the aircraft. There's other bad news to report on funding for hurricane research, which I'll report in a later blog.

Jeff Masters

Storms and heat in Europe

By: JeffMasters, 4:04 PM GMT on January 19, 2007

Europe's strange winter weather continues to generate headlines, as a powerful low pressure system brought hurricane-force wind gusts to England, Germany, the Czech Republic, and many other European countries on Thursday. The powerful extratropical cyclone, now centered over western Russia, has a central pressure of 960 mb--the kind of pressures commonly seen in Category 1 and 2 hurricanes! At least 41 people have been killed in the storm, mostly motorists in England and Germany. The storm shut down the German train system for the first time in history. The last winter storm with comparable winds in Europe occurred in January 1990. The latest computer forecast models point to the first significant snows and cold for Europe next week, when a major low pressure system is expected to finally tap into some cold Artic air and pull it southwards over much of Europe.

Figure 1. Departure of temperature from average (in �C) for the week (Sun-Thu). The western U.S. is suffering the worst winter cold of anywhere in the Northern Hemisphere. Europe and northern Asia continue to feel record-breaking warm temperatures. Note that the area of most extreme below-normal temperatures occurred over San Antonio, Texas, where the world's largest meeting of meteorologists was being held!

Extraordinary warmth in Europe
The European storm was a warm and rainy one, and record warmth continues to affect both Europe and most of northern Asia (Figure 1). January 10, with a temperature of 8 �C, was the warmest in the first 10 days of January in Moscow, Russia, according to the hydro-meteorological bureau for Moscow. Record keeping began in 1870. St. Petersburg reported their warmest January day in 125 years of record keeping the same day, with a temperature of 8.6 �C. Nighttime minimum temperatures in London, England, hit 12.6 �C on January 8, which is warmer than the average July minimum temperature, 12� C. So far, January temperatures in London are the warmest since record keeping began in 1659.

Romanian snowboarders blockade weather office
The lack of snow in Romania has driven snow lovers in that country to desperation. A group of Romanian snowboarders blocked traffic in front of the country's weather institute January 16, and would only budge when weather officials would agree that their complaints of a lack of snow "would be passed on to a higher authority", according to Ananova.

Winter hits the U.S., China, and Bengladesh
Winter cold has hit the western U.S. hard this week, with California suffering a devastating freeze to its citrus crop. Heavy snow has affected central China--the Chinese official state media Xinhua said on January 16th that more than 1,000 houses have collapsed and 2,424 damaged in the weather as snow levels reached 300 millimeters in some regions. Earlier this month, Bengladesh saw temperatures that fell from the daily average of 18 �C to between 5 and 8 �C. The government called on affluent people to donate warm clothes and blankets to the poor, as doctors reported that more than 100 people had died from the sudden cold.

Jeff Masters

Winter Weather

The big weather meeting

By: JeffMasters, 4:34 AM GMT on January 17, 2007

Greetings from the annual meeting of the American Meteorological Society in San Antonio, Texas! At the world's largest gathering of meteorologists, the main topic of conversion has been--drum roll--the weather! Mostly, we�ve been grumbling about the nasty ice storm here, which has left city streets deserted and given the local school kids a holiday. Why couldn�t our record warm winter weather have lasted another week?! The large-scale weather pattern over the Northern Hemisphere has indeed changed to a decidedly wintery one, not only for North America, but northern Asia as well. Even Europe appears likely to get some real winter weather starting next week. I speculate that part of the reason for this shift is that the Arctic ice has finally frozen up enough to cut off the extra heat and moisture that was retarding formation of the usual cold Arctic air masses at the beginning of winter. Natural variability of the weather is probably the major factor, though.

Figure 1. Global departure of temperature from average for December 2006. Image credit: NCDC.

The other big topic of conversation has been the unbelievably warm winter we�ve had up until now. Talks I�ve attended given by meteorologists from both the U.S. and Europe have emphasized how unusual this winter was--and most of 2006. Take a look at the newly-released image (Figure 1) of the warmest December on record for the globe. The average global temperature for December 2006 was +0.72�C (+1.30�F) above normal, beating out 2003's record of +0.70�C/1.26�F, according to the National Climatic Data Center. Much of the U.S., Canada, Europe, and Siberia recorded their warmest December ever. Below normal temperatures were recorded in the Middle East and northern Africa, but over 80% of the world�s land areas were warmer than average--and not just a little above average! The swath of temperatures more than 5�C (9 �F) above average covering most of the world�s land mass north of 40� north latitude is unprecedented in size in the wintertime historical record, going back to at least 1900.

Record winter warmth in one part of the Northern Hemisphere is usually due to a sharp bend in the jet stream that creates a ridge of high pressure, allowing a warm southerly flow of air into the region. Adjacent regions have a compensating trough of low pressure that brings cold, northerly winds and below normal temperatures. This was certainly the case in January 2006, when the U.S. experienced its warmest January on record. Asia and Europe experienced a brutally cold January. Moscow hit -40�, its coldest temperature since 1979. Parts of Portugal saw their first snow since 1954. Siberia reached -70� F.

Enter December 2006. Again, record warmth was observed over the U.S. and Canada. A compensating cooler than normal area was present over the Gulf of Alaska and western Siberia, but it was very weak. There was almost no cold Arctic air present anywhere in the Northern Hemisphere, which is unprecedented in the historical record (going back at least 100 years). What�s the cause of this unusual pattern? Part of the blame probably rests with the late-freezing Arctic ice this year. More open water than ever recorded pumped abnormal heat and moisture into the air, retarding the formation of the usual cold air masses. At an interesting talk titled �Extremes and El Nino� given by Dr. Gerald Meehl of the National Center for Atmospheric Research today, he showed that both El Nino and increasing greenhouse gases are probably part of the reason, as well. He averaged together the wintertime temperature anomalies for El Nino events for the 1970s through 1990s, and came up with a plot that showed the typical pattern we expect--a warm winter over Canada and the northern U.S., and cold over Europe and Asia. Next, he showed a climate model simulation of a wintertime El Nino event run using the levels of greenhouse gases that we have now. The model simulation showed wintertime warmth extending into Asia and Europe during El Nino years, much like the pattern in Figure 1, thanks to the increase in greenhouse gases over the past 30 years.

In other talks I heard today, Dr. Roger Brugge of the University of Reading in England estimated that the record warm temperatures measured in parts of Europe this fall would be repeated only once in 5,000-10,000 years, unless climate change were to blame. Dr. Klaus Wolter of NOAA remarked, �We all know global change is occurring,� and went on to say, �the gun is starting to smoke�, when analyzing the persistent increasing trend in extremely warm events in the Northern Hemisphere.

One cannot blame a single weather event�or single warm year�on climate change. However, the unbelievably warm start to the winter of 2006-2007 is part of an unmistakable pattern that shows human-caused climate change is upon us.

Jeff Masters

Climate Change

Global cooling

By: JeffMasters, 12:24 AM GMT on January 15, 2007

Global temperatures in 2006 were the third coldest on record in the lower stratosphere, according to the National Climatic Data Center. Only 1997 and 2000 had colder temperatures since record keeping began in 1979 (Figure 1). Why is this important? Well, the stratosphere is that layer of the upper atmosphere approximately 14-22 km (9-14 miles) above the surface that contains our protective ozone layer. The main reason for the recent stratospheric cooling is due to the destruction of ozone by human-emitted CFC gases. Ozone absorbs solar UV radiation, which heats the surrounding air in the stratosphere. Loss of ozone means that less UV light gets absorbed, resulting in cooling of the stratosphere. Cooling of the stratosphere results in the formation of more polar stratospheric clouds, which require very cold temperatures to form. The presence of these clouds allows even more ozone destruction to occur, since the reactions responsible for ozone destruction occur much faster in clouds than in dry air. Thus, the recent cooling of the stratosphere allows high levels of harmful UV light to reach the surface. As CFC gases begin to decline in coming years thanks to banning of these substances in 1987, the stratosphere should start to warm, and ozone levels will recover.

Figure 1. Global lower stratospheric departure of temperature from average since 1979, as measured by satellites. The large spikes in 1982 and 1991 are due to the eruptions of El Chicon and Mt. Pinatubo, respectively. These volcanos ejected huge quantities of sulphuric acid dust into the stratosphere. This dust absorbed large quantities of solar radiation, heating the stratosphere. Image credit: National Climatic Data Center.

Greenhouse gases also cause stratospheric cooling
However, this recovery of the ozone layer is being delayed. A significant portion of the observed stratospheric cooling is also due to human-emitted greenhouse gases like carbon dioxide and methane. Climate models predict that if greenhouse gases are to blame for heating at the surface, compensating cooling must occur in the upper atmosphere. We need only look as far as our sister planet, Venus, to see the truth of this theory. Venus's atmosphere is 96.5% carbon dioxide, which has triggered a run-away greenhouse effect of truly hellish proportions. The average surface temperature on Venus is a very toasty 894°F! However, Venus's upper atmosphere is a startling 4-5 times colder than Earth's upper atmosphere. The explanation of this greenhouse gas-caused surface heating and upper air cooling is not simple, but good discussions can be found at Max Planck Institute for Chemistry and for those unafraid of radiative transfer theory. One way to think about the problem is that the amount of infrared heat energy radiated out to space by a planet is roughly equal to the amount of solar energy it receives from the sun. If the surface atmosphere warms, there must be compensating cooling elsewhere in the atmosphere in order to keep the amount of heat given off by the planet the same. As emissions of greenhouse gases continue to rise, their cooling effect on the stratosphere will increase. This will make recovery of the stratospheric ozone layer much slower.

Greenhouse gases cause cooling higher up, too
Greenhouse gases have also led to the cooling of the atmosphere at levels higher than the stratosphere. Over the past 30 years, the Earth's surface temperature has increased 0.2-0.4°C, while the temperature in the mesosphere, about 50-80 km above ground, has cooled 5-10°C (Beig et al., 2006). There is no appreciable cooling due to ozone destruction at these altitudes, so nearly all of this dramatic cooling is due to the addition of greenhouse gases to the atmosphere. Even greater cooling of 17°C per decade has been observed high in the ionosphere, at 350 km altitude. This has affected the orbits of orbiting satellites, due to decreased drag, since the upper atmosphere has shrunk and moved closer to the surface (Lastovicka et al., 2006). The density of the air has declined 2-3% per decade the past 30 years at 350 km altitude. So, in a sense, the sky IS falling!

What about global warming being caused by the sun?
Some scientists have theorized that increases in solar output are responsible for a significant portion of the observed global warming. For instance, Scafetta & West (2006) estimated that 25-35% of the global warming in the 1980-2000 period was attributable to solar variability. Other scientists disagree, finding no evidence of global warming due to solar activity changes since the 1940s. Since any increase in solar radiation would heat both the lower and upper atmosphere, the observed drop in upper atmospheric temperatures in the past 30 years argues against a large portion of the observed greenhouse effect being caused by solar variability. The observed cooling of the upper atmosphere in recent decades is strong evidence that the warming at Earth's surface is due to human-emitted greenhouse gases. It should also give us additional confidence in the climate models, since they predicted that this upper atmospheric cooling would occur.

I'll be at the annual meeting of the American Meteorological Society in San Antonio this week, and plan to post a blog from there Wednesday.

Jeff Masters

Climate Change

El Nio is fading

By: JeffMasters, 4:28 PM GMT on January 12, 2007

El Nio has peaked and is likely to slowly decline over the coming months, according to the latest forecasts issued by NOAA and the Australian Bureau of Meteorology. The strength of an El Nio is gauged by how warm the Equatorial Pacific waters off the coast of South America get. These Sea Surface Temperatures (SSTs) peaked at 1.2 C above average in late November, and stayed high through December, as a surge of westerly winds pushed warm water to the coast of South America. The winds at the surface have turned more easterly in the past two weeks, which has allowed the SSTs to cool dramatically (Figure 1). It is still possible that one more surge in westerly winds might reinforce the warm waters at the South American coast, but the consensus of the El Nio computer forecast models is that this El Nio is all done. This is the usual time of year that El Nio begins to fail, and we can expect a slow return to neutral conditions over the next six months. By August, expect SSTs off the coast of Peru to drop below 0.5 C above average, the threshold for an El Nio. The way SSTs have dropped in the past week, the demise of El Nio could come much sooner, perhaps by June. In any case, El Nio will probably not die fast enough to significantly alter the weather patterns we've seen this winter. Expect continued above normal temperatures in North America and Europe, dry conditions in Australia and Indonesia, and wet weather in Peru and southern Brazil for the next two months.

Figure 1. Departure of Sea Surface Temperature (SST) from average for the week centered on December 27, 2006 (top) and January 3, 2007 (bottom). Images taken from a 12-week SST animation courtesy of NOAA's Climate Prediction Center.

The demise of El Nio is bad news for those affected by the Atlantic hurricane season. El Nio conditions substantially dampen hurricane activity in the Atlantic, and the return to El Nio-neutral conditions by August could make for an active hurricane season. The pre-season Atlantic hurricane season forecast for 2007 issued by Bill Gray's team at Colorado State anticipated the demise of El Nio for 2007. The forecast calls for 14 named storms, 7 hurricanes, and 3 intense hurricanes (an average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes). An above normal chance of a major hurricane hitting the U.S. is seen, both along the East Coast (40% chance, 31% chance is normal) and the Gulf Coast (40% chance, 30% chance is average). The good news for those of you affected by Atlantic hurricanes is that tropical Atlantic SSTs have decreased substantially during the past few months. These SSTs were about 1.0 C above normal in October, but have fallen to about 0.5 C above normal. Comparison of the SSTs this winter in December vs. last winter (Figure 2) shows that temperatures are 0 - 0.5 C warmer in the Caribbean this winter, but about 0.5 C cooler between Africa and the Lesser Antilles. That's still plenty of extra heat to fuel the hurricanes of 2007, but the downward trend in SSTs over the Atlantic this winter is encouraging.

Figure 2. The difference in Sea Surface Temperature (SST) from December 2006 to December 2005. Blue and purple colors denote where it is colder this winter than last winter. Image credit: NOAA.

Snow in New York City!
Well, it wasn't much. A few flurries whitened the skies over New York City on Wednesday January 10, bringing an official trace of snow to the city. It was the first trace of snow this winter for the city, breaking the record set in 1877-1878, when the first trace arrived on January 4. New York City's first chance at accumulating snow doesn't appear likely to happen until January 22, at the earliest.

Jeff Masters

2006: warmest year on record in the U.S.

By: JeffMasters, 9:18 PM GMT on January 09, 2007

The United States recorded its warmest year ever in 2006, according to today's report issued by the National Climatic Data Center (NCDC). The 2006 annual average temperature was 55�F, 2.2�F (1.2�C) above the 20th Century mean and 0.07�F (0.04�C) warmer than the previous warmest year, 1998. The NCDC had estimated that 2006 would be the 3rd warmest year in U.S. history last month, but an unusually warm December pushed 2006 to the top. It was the warmest December on record in the Northeast U.S., and the 4th warmest December for the country as a whole. Only 1939, 1957, and 1933 had warmer Decembers. However, the statistics partially hide the extraordinary warmth that began on December 10 and continued until January 6, when New York City tied their all-time record January high temperature of 72�. During the month ending January 6, the Northeast was 14 �F above average, and the U.S. as a whole was 7� above average.

No cause for alarm?
"No cause for alarm. Enjoy it while you have it," said Mike Halpert, head of forecast operations at the National Oceanic & Atmospheric Administration's Climate Prediction Center, in a story run by CNN just before New York City's record warmth. The story continued, "The weather is prone to short-term fluctuations, and forecasters said the mild winter does not necessarily mean global warming is upon us. In fact, the Plains have been hit by back-to-back blizzards in the past two weeks." True, the weather across most of the U.S. has finally cooled off this week, and the rest of January should have near average temperatures. And I agree that one warm month of winter in one country in its warmest year in 112 years of record keeping is not evidence of global warming, particularly when there is a moderate El Nino episode going on. An El Nino can lead to significantly warmer winters in the U.S.--exceptional December warmth has also occurred in 1877, 1939, and 1957, all of which were moderate or strong El Nino years. I've plotted up a comparison of temperatures in December of 1957 vs 2006 (Figure 1), and one can see that the unusual warmth of December 2006 does have historical precedent. Taking a look at average U.S. December temperatures for all years in the historical record (Figure 2), we see that these temperatures do show quite a bit of noise, and there is no evidence of dramatic warming in the past 30 years.

Figure 1. Comparison of the departure of average temperature from normal for December 1957 (the the second warmest December on record in the U.S.) and December 2006. Image credit: NOAA.

Figure 2. Average December temperatures for the U.S. from 1895 to 2006. Image credit: National Climatic Data Center.

Rolling thirteens with the weather dice
Take a look at the trend December temperatures in Figure 2. It shows that the average temperature has warmed a little more than 1� F in the past century. It may not seem like much, but that is enough to significantly load the dice in favor of warmer winters. Six of the ten warmest U.S. winters on record have occurred in the past 15 years. Month long spells where winter is seemingly absent--as also occurred in January 2006, the warmest January in U.S. history--have become more common. Keep in mind that the weather of January of 2006--which blew away the previous record for warmest January by a huge margin (2� F)--occurred during a La Nina year, not an El Nino. What concerns me most is that the warming trend is not isolated to the U.S. The 1� F rise in temperatures the past century has occurred world-wide, thanks to global warming, and the temperature increase has been much higher in the Arctic--something the climate models have predicted would occur as a telltale sign of the human-caused addition of greenhouse gases to the atmosphere. In the past, an exceptionally warm winter month in the U.S., like December 1957 (Figure 3), was offset by much cooler weather elsewhere, such as we see in Alaska, Greenland, and northern Siberia. However, December 2006 had no such offsetting cool temperatures--it was more than 1� C above average over almost all the land areas of the Northern Hemisphere north of 40� north latitude (Figure 4). Colorado, whose three blizzards have been widely cited as evidence that winter has been severe elsewhere, still recorded temperatures about 1� C above normal in December 2006.

Figure 3. Global departure of temperature from average for December 1957, the second warmest December on record in the U.S. Note that the exceptionally warm temperatures over the U.S. are offset by much cooler weather elsewhere, such as in Alaska, Greenland, and northern Siberia.

Figure 4. Global departure of temperature from average for December 2006. Note that the almost the entire globe north of 40� north latitude was more than 1� C above average, with large areas more than 6� C (11� F) above average.

All this unusual heat in the northern high latitudes is going to significantly slow down the formation of ice over the Arctic Ocean this winter. Furthermore, the lack of the usual snows across the Arctic may allow the snowpack to melt much earlier than normal in spring, resulting in more record warmth in the Arctic this summer. Arctic sea ice coverage, already down 20% in the past 20 years, is likely to continue to shrink in 2007. As sea ice melts in response to rising temperatures, it creates a positive feedback loop: melting ice means more of the dark ocean is exposed, allowing it to absorb more of the sun's energy, further increasing air temperatures, ocean temperatures, and ice melt. The observed changes in the ice cover (Figure 5) indicate that this feedback is now starting to take hold, and the weather dice will continue to get more loaded towards rolling higher numbers in 2007. I do think we're due for a cold winter next year--part of the warmth of the past two winters is probably due to the normal random fluctuations in the weather, and Nature has been rolling twelves more often than snake eyes of late. However, we're not going to see snake eyes too much more. December's weather in the Northeast U.S. may have been a case of the weather dice coming up thirteen--weather not seen on the planet since before the Ice Age began, 118,000 years ago. The weather dice will start rolling an increasing number of thirteens in coming years, and an ice-free Arctic Ocean in summertime by 2040 is a very real possibility, as indicated by computer modelling studies published in the Journal of Geophysical Research last month. This possibility is cause for alarm, and I, for one, had a lot of trouble enjoying the phenomenally warm weather of the past month here in Michigan.

Figure 5. Percent change in coverage of Arctic sea ice in Decembers from 1979-2006, compared to the 1979-2000 average. The Polar Ice Cap has shrunk by about 15% in December, and 20% in summer, over the past 20 years. Image credit: National Snow and Ice Data Center.

Check out the post on this winter's anomalous warmth.

I'll be back Thursday afternoon or Friday with a look at the status of El Nino. Will it still be around during hurricane season?

Jeff Masters

Climate Change Climate Summaries

72° in New York City; Avalanche rips Colorado highway

By: JeffMasters, 8:12 PM GMT on January 06, 2007

The heat is on in New York City! The temperature soared to 72° at New York's Central Park Saturday, tying their all-time warmest January temperature ever. New York City has hit 70 degrees in January only twice before since record keeping began in 1869--on January 4, 1932 (70°), and on January 26, 1950 (72°). The 72° reading is a full 34° above their normal high of 38. Records were smashed all over the Northeast today. Philadelphia reached 73° and Newark hit 72°. The all time record for January warmth was 74 °in both cities, set on January 26, 1950. Hartford, Connecticut hit 72,° besting their warmest January temperature ever--70, °set on January 14, 1932. How unusual is this winter? La Guardia airport broke their all-time record for the date (59) °at 6am this morning, when the minimum temperature is usually measured! La Guardia went on to post their warmest January temperature ever, 72°. New York City has not seen a single flake of snow this winter, surpassing the winter of 1877-1878 for the longest stretch without snow (a trace of snow was finally measured on January 4, 1878 that winter). New York City averages 22.4 inches of snow per year. While the current weather forecast does show some colder air moving into New York and most of the U.S. over the next week, no snow is forecast for New York City for at least another week.

The reason for the warmth? A moderate El Nino event is adding a tremendous amount of heat to the globe this winter, and has helped displace the jet stream farther to the north than usual. Global warming is also partly to blame, along with natural variability in the Earth's weather. I also believe that the on-going melting of the Arctic Ice Cap may have contributed to this winter's warmth, although it is difficult to know how much so without doing detailed model studies. Record low levels of sea ice in the Arctic in November and December have exposed much larger areas of open water than usual. The open ocean water provides a tremendous source of heat to the atmosphere, and the extra moisture from the open ocean areas creates cloud cover that insulates the surface. This has allowed less cold Arctic air than usual to form over the Northern Hemisphere. However, now that we are well into the coldest part of winter, the Arctic sea ice has frozen up more. This, combined with the natural cooling due to the 24-hour darkness that continues over the pole, is allowing a large area of cold air to form over the pole. The latest runs of the GFS computer model show that this Arctic air will plunge southwards over North America during the next two weeks, bringing near-normal winter conditions to the U.S. and Canada during the second and third weeks of January. However, exceptionally warm conditions will continue over most of Europe and Asia during this period.

Colorado's tough winter continues: huge avalanche buries cars
Denver's third major snowstorm of the winter brought up to 8 inches of snow to the Denver area today. The heavy snow triggered a major avalanche 60 miles west of Denver that buried a 200-foot wide section of U.S. Highway 40 to a depth of 15 feet. Two cars plunged over the edge, but all eight people inside were rescued. The avalanche occurred near 11,307-foot-high Berthoud Pass. Colorado has had a lot snow, thanks to a kink in the jet stream that has put the predominant storm track over the state. However, the weather has not been very cold--the average temperature in Denver during December was 1.4° above normal, thanks to warm weather that moved into the region before and after each major storm. About 95% of the U.S. had above-normal temperatures in December.

2007 to be warmest year on record?
There is a 60% chance that 2007 will be the warmest year on record, according to a forecast issued by the United Kingdom Meteorological Office on January 4. The forecasters cited the combined influence of the continuing global warming trend, and the presence of a moderate El Nino event. "Even a moderate (El Nino) warming event is enough to push the global temperatures over the top," said Phil Jones, director of the Climatic Research unit at the University of East Anglia. The warmest years on record were 2005 and 1998, when the global average temperature was 1.2°F higher than the long-term average of 57°F. Given the remarkable warmth across not only North America this January, but also Europe and Asia, I think that a 40% chance of a warmest year ever is a reasonable forecast, but 60% might be too high. Not all El Nino events create a big increase in global temperatures.

I'll talk more about the amazing warmth of this winter on Tuesday afternoon, when the National Climatic Data Center releases their U.S. statistics for December of 2006.

Jeff Masters

Climate Change Winter Weather

2006 in review: the global tropical cyclone season

By: JeffMasters, 2:08 PM GMT on January 04, 2007

While no records were set in any ocean basin for number of tropical cyclones or number of intense tropical cyclones, 2006 saw a number of remarkable storms. Here's a summary of the most notable storms of the year, and the hardest hit countries:

Most intense tropical cyclone of 2006: Cyclone Monica.
Tropical Cyclone Monica, which made landfall on the sparsely populated northern coast of Australia in April, was the most intense tropical cyclone of 2006. The Joint Typhoon Warning Center estimated maximum sustained winds of 180 mph with gusts to 220 mph at 00 GMT April 24, and a minimum pressure of 879 mb. However, other satellite measurements of Monica's peak intensity were different--TCWC Darwin reported a minimum pressure of 905 mb at 5:00pm ACST (0730 UTC) on April 23, and an unofficial estimate from the University of Wisconsin put Monica's lowest pressure at 868.5 mb--1.5 mb lower than the world record low pressure observed in Super Typhoon Tip of 1979. Monica brought a 5-6 meter (16-20 foot) storm surge to the coast when it made landfall, and Margie Kieper's View From the Surface blog from yesterday has an impressive photo of the incredible damage Monica did to the forest on the Australian coast.

Monica was the most intense cyclone ever observed in the Southern Hemisphere, which is remarkable, given that she formed in the last half of April, when the Australian cyclone season is typically over. The co-record holder, also with a minimum pressure of 879 mb, is held by Cyclone Zoe of 2002, a Category 5 storm that affected several small islands in the Solomon chain. Reliable records of Southern Hemisphere cyclones only go back to the 1980s, so it is likely that there were other storms with lower pressures in the Southern Hemisphere during the past century. The lowest pressure measured at the surface in a Southern Hemisphere cyclone was 905 mb at North Rankin A gas platform during Cyclone Orson on 22-23 April 1989. Orson had 160 maximum sustained winds at the time, making it a Category 5 storm.

Figure 1. Eye of Tropical Cyclone Monica at 0430 GMT April 24 2006. Image credit: NASA.

Hardest hit country in 2006: the Philippines
The 2006 typhoon season saw an unprecedented five major (Category 3 or higher) typhoons make landfall in the Philippines, plus one Category 2 storm. Officially, 2049 people are listed as dead or missing and presumed dead from the 2006 typhoon season. Another 1122 died after monsoon rains triggered a landslide that buried the entire village of Guinsaugon in the central island of Leyte in February. In all, the six typhoons caused about $1.3 billion in damage--the most damaging typhoon season in Philippine history. For comparison, damage from all Philippine typhoons in the 20th century was $5.6 billion.

Figure 2. The fearsome sixsome of Philippine typhoons in 2006. From upper left to upper right: Super Typhoon Chanchu (May, Category 2 at landfall); Super Typhoon Xangsane (Category 4, September); Super Typhoon Cimaron (Category 5, October). From lower left to lower right: Typhoon Chebi (November, Category 3); Super Typhoon Durian (November, Category 4); Typhoon Utor (December, Category 3). A Super Typhoon is any storm with sustained 1-minute average winds of 150 mph or greater.

Deadliest tropical cyclone of 2006: Super Typhoon Durian
Super Typhoon Durian was the worst of the Philippine typhoons in 2006. Durian initially hit the island of Catanduanes as a Category 4 typhoon with sustained winds of 145 mph. Virtually every building on the island was damaged or destroyed, and Durian was judged the worst typhoon ever to hit the island. Next, Durian powered ashore into extreme southern Luzon Island in the province of Albay, still packing Category 4 winds of at least 135 mph. Durian passed directly over Mayon, the most active volcano in the Philippines and one of the country's most famous tourist attractions because of its near-perfect cone. Loose rock that the volcano had deposited in a July eruption rushed down the slopes in the form of deadly mudslides, thanks to Durian's torrential rains. Estimates from NASA's TRMM satellite of the rain amounts were 8-12 inches in a 24 hours period. The mudslides swept into villages and rivers at the foot of the Mayon Volcano. At least 1479 people died in the Philippines, mostly in mudslides near the Mayon volcano. This was the third deadliest typhoon in Philippine history, and the most damaging. Durian destroyed 211,000 homes, and damaged another 308,000. Durian weakened to a Category 1 typhoon after it emerged in the South China Sea, and passed along the coast of southern Vietnam. Durian killed 95 more people in Vietnam, destroying 50,000 homes and damaging 195,000. Damage was estimated at $456 million in Vietnam.

Most damaging tropical cyclone of 2006: Cyclone Larry
Australia got hit exceptionally hard by tropical cyclones in 2006, suffering hits by three major cyclones--Category 5 Monica in April, Category 3 Glenda in March, and the worst blow, Cyclone Larry on March 20, 2006. Cyclone Larry was a borderline Category 3/4 storm on the U.S. Saffir/Simpson scale, and struck Queensland with a fury unmatched in that region in perhaps a century. Damage from the storm was estimated at over $1 billion U.S. dollars.

Figure 3. Cyclone Larry. Image credit: NASA.

Longest duration intense tropical cyclone in history: Ioke
Hurricane Ioke (a.k.a. Super Typhoon Ioke after it crossed the Date Line) was the strongest hurricane ever recorded in the Central Pacific, and remained at Category 4 or 5 strength longer than any tropical cyclone on record. Ioke spent 36 (33 consecutive) 6-hourly reports at that strength. The previous records were held by 2004's Hurricane Ivan with 33 (32 consecutive) and 1997's Typhoon Paka with 27 (25 consecutive) 6-hourly reports. The Accumulated Cyclone Energy (ACE) for this one storm was about 81--higher than the ACE index of 79 accumulated by all the tropical cyclones in the Atlantic 2006 hurricane season.

Figure 4. Super Typhoon Ioke. Image credit: NASA.

Jeff Masters

The global hurricane season of 2006: was it unusual?

By: JeffMasters, 2:22 PM GMT on January 03, 2007

The year 2006 is in the books, and its time to review the notable tropical cyclones of the year. For the first time since 1997, there was little to talk about in the Atlantic. The only Atlantic storm of significance was Hurricane Ernesto, which killed five people in Haiti and did $500 million in damage to the U.S. East Coast. The action was much more intense in the Eastern Pacific, which saw 20 named storms (16 is average) and six major hurricanes (4.5 is average.) The Pacific coast of Mexico was pounded by three tropical cyclones in 2006: Hurricane John hit Baja as a Category 2 hurricane, killing 5; Hurricane Lane hit north of Mazatlan as a Category 3 hurricane, killing 4; and Tropical Storm Paul hit the same region, killing four. Also notable, although it did not affect land, was Hurricane Sergio. It formed in mid-November and grew to Category 2 strength, becoming the strongest Northeast Pacific hurricane so late in the season and the longest-lived November tropical cyclone on record in that ocean basin.

Figure 1. Tropical Storm Ernesto just before landfall in North Carolina, August 31, 2006.

Figure 2. Statistics for the global tropical cyclone season of 2006. The three numbers in each box represent the actual number observed in 2006, followed by the average for the period 1970-2005 (in parentheses), followed by the record from the same period (in red).

Looking at the statistics for the season (Figure 2), 2006 appears to be a fairly normal year. No records were set for tropical cyclone activity in any ocean basin. Was it was a good year for the proponents of the theory that global warming is causing an increase in strong hurricanes? Twenty-nine major hurricane formed in 2006, just one shy of the record of 30, and 21 Category 4 and 5 storms formed, half way between the average of 17 and the record high of 25. These numbers are similar to those of 2005, which had 27 major storms and 22 Category 4 and 5 storms. However, as reported in a Science article by Landsea et. al in July, the number of Category 4 and 5 storms between 1978-1990 globally may have been undercounted by 70 storms. If true, this would bring the statistics for 2005 and 2006 closer to average for these most powerful of tropical cyclones. A new policy statement regarding the unproven link between stronger hurricanes and climate change was adopted by the World Meteorological Organization in December, in response to the recommendations of a meeting of 125 hurricane researchers that attended a meeting in Costa Rica. The summary statement (which I agree with) is posted at the World Meteorological Organization web site, and the ten main points are presented below. There is also a detailed statement with references to the scientific literature available at the WMO web site.

Consensus Statements by International Workshop on Tropical Cyclones-VI (IWTC-VI) Participants:

The surfaces of most tropical oceans have warmed by 0.25 - 0.5°C during the past several decades. The Intergovernmental Panel on Climate Change (IPCC) considers that the likely primary cause of the rise in global mean surface temperature in the past 50 years is the increase in greenhouse gas concentrations. The global community of tropical cyclone researchers and forecasters as represented at the 6th International Workshop on Tropical Cyclones of the World Meteorological Organization has released a statement on the links between anthropogenic (human-induced) climate change and tropical cyclones, including hurricanes and typhoons. This statement is in response to increased attention on tropical cyclones due to the following events:

a) There have been a number of recent high-impact tropical cyclone events around the globe. These include 10 landfalling tropical cyclones in Japan in 2004, five tropical cyclones affecting the Cook Islands in a five-week period in 2005, Cyclone Gafilo in Madagascar in 2004, Cyclone Larry in Australia in 2006, Typhoon Saomai in China in 2006, and the extremely active 2004 and 2005 Atlantic tropical cyclone seasons - including the catastrophic socio-economic impact of Hurricane Katrina.

b) Some recent scientific articles have reported a large increase in tropical cyclone energy, numbers, and wind-speeds in some regions during the last few decades in association with warmer sea surface temperatures. Other studies report that changes in observational techniques and instrumentation are responsible for these increases.

1. Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.

2. No individual tropical cyclone can be directly attributed to climate change.

3. The recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.

4. Tropical cyclone wind-speed monitoring has changed dramatically over the last few decades, leading to difficulties in determining accurate trends.

5. There is an observed multi-decadal variability of tropical cyclones in some regions whose causes, whether natural, anthropogenic or a combination, are currently being debated. This variability makes detecting any long-term trends in tropical cyclone activity difficult.

6. It is likely that some increase in tropical cyclone peak wind-speed and rainfall will occur if the climate continues to warm. Model studies and theory project a 3-5% increase in wind-speed per degree Celsius increase of tropical sea surface temperatures.

7. There is an inconsistency between the small changes in wind-speed projected by theory and modeling versus large changes reported by some observational studies.

8. Although recent climate model simulations project a decrease or no change in global tropical cyclone numbers in a warmer climate, there is low confidence in this projection. In addition, it is unknown how tropical cyclone tracks or areas of impact will change in the future.

9. Large regional variations exist in methods used to monitor tropical cyclones. Also, most regions have no measurements by instrumented aircraft. These significant limitations will continue to make detection of trends difficult.

10. If the projected rise in sea level due to global warming occurs, then the vulnerability to tropical cyclone storm surge flooding would increase.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Category 6™


Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather