The number of Category 4 and 5 hurricanes worldwide has nearly doubled over the past 35 years, even though the total number of hurricanes has dropped since the 1990s, according to a study by researchers at the Georgia Institute of Technology and the National Center for Atmospheric Research (NCAR). The shift occurred as global sea surface temperatures have increased over the same period. The research appears in the September 16 issue of Science.

Peter Webster, professor at Georgia Tech’s School of Earth and Atmospheric Sciences, along with NCAR’s Greg Holland and Georgia Tech’s Judith Curry and Hai-Ru Chang, studied the number, duration, and intensity of hurricanes (also known as typhoons or tropical cyclones) that have occurred worldwide from 1970 to 2004. The study was supported by the National Science Foundation (NSF), NCAR’s primary sponsor.

“What we found was rather astonishing,” said Webster. “In the 1970s, there was an average of about 10 Category 4 and 5 hurricanes per year globally. Since 1990, the number of Category 4 and 5 hurricanes has almost doubled, averaging 18 per year globally.”

Category 4 hurricanes have sustained winds from 131 to 155 miles per hour; Category 5 systems, such as Hurricane Katrina at its peak over the Gulf of Mexico, feature winds of 156 mph or more.
Katrina damage
Greg Holland. (Photo by Carlye Calvin.)

“This long period of sustained intensity change provides an excellent basis for further work to understand and predict the potential responses of tropical cyclones to changing environmental conditions”, said NCAR’s Holland.

“Category 4 and 5 storms are also making up a larger share of the total number of hurricanes,” said Curry, chair of the School of Earth and Atmospheric Sciences at Georgia Tech and coauthor of the study. “Category 4 and 5 hurricanes made up about 20% of all hurricanes in the 1970s, but over the last decade they accounted for about 35% of these storms.”

The largest increases in the number of intense hurricanes occurred in the North Pacific, Southwest Pacific, and the North and South Indian Oceans, with slightly smaller increases in the North Atlantic Ocean.

All this is happening as sea surface temperatures have risen across the globe between one-half and one degree Fahrenheit, depending on the region, for hurricane seasons since the 1970s.

“Our work is consistent with the concept that there is a relationship between increasing sea surface temperature and hurricane intensity,” said Webster. “However, it’s not a simple relationship. In fact, it’s difficult to explain why the total number of hurricanes and their longevity has decreased during the last decade, when sea surface temperatures have risen the most.”

“NCAR is now embarking on a focused series of computer experiments capable of resolving thunderstorms and the details of tropical cyclones,” said Holland. “The results will help explain the observed intensity changes and extend them to realistic climate change scenarios.”

The only region that is experiencing more hurricanes and tropical cyclones overall is the North Atlantic, where they have become more numerous and longer-lasting, especially since 1995. The North Atlantic has averaged eight to nine hurricanes per year in the last decade, compared to six to seven per year before the increase. Category 4 and 5 hurricanes in the North Atlantic have increased at an even faster clip: from 16 in the period of 1975-89 to 25 in the period of 1990-2004, a rise of 56%.

A study published in July in the journal Nature came to a similar conclusion. Focusing on North Atlantic and North Pacific hurricanes, Kerry Emanuel (Massachusetts Institute of Technology) found an increase in their duration and power, although his study used a different measurement to determine a storm’s power.

But whether all of this is due to human-induced global warming is still uncertain, said Webster. “We need a longer data record of hurricane statistics, and we need to understand more about the role hurricanes play in regulating the heat balance and circulation in the atmosphere and oceans.”

“Basic physical reasoning and climate model simulations and projections motivated this study,” said Jay Fein, director of NSF’s climate and large scale dynamics program, which funded the research. “These results will stimulate further research into the complex natural and anthropogenic processes influencing these tropical cyclone trends and characteristics.”

Webster is currently attempting to determine the basic role of hurricanes in the climate of the planet. “The thing they do more than anything is cool the oceans by evaporating the water and then redistributing the oceans’ tropical heat to higher latitudes,” he said.

“But we don’t know a lot about how evaporation from the ocean surface works when the winds get up to around 100 miles per hour, as they do in hurricanes,” said Webster, who adds that this physical understanding will be crucial to connecting trends in hurricane intensity to overall climate change.

“If we can understand why the world sees about 85 named storms a year and not, for example, 200 or 25, then we might be able to say that what we’re seeing is consistent with what we’d expect in a global warming scenario. Without this understanding, a forecast of the number and intensity of tropical storms in a future warmer world would be merely statistical extrapolation.”

Original press release: Hurricanes Are Getting Stronger, Study Says (UCAR)

Until now satellites have not been able to monitor melting of ice at the very point where it is most significant: at the ice edge. CryoSat’s ability to do just that thrills scientists working in the field.

“CryoSat will pave the way for a better understanding of what happens to the ice at the exact point where things are the most interesting: at the ice edge where the majority of the melting takes place,” says Danish glaciologist Carl Egede Bøggild.

Part of the Geological Survey of Denmark and Greenland (GEUS) Bøggild heads a large-scale monitoring programme on the Greenland Ice. The programme utilises a combination of on-site measurements and satellite data.

“In principle you would prefer satellite data when you want to monitor large-scale developments,” explains Bøggild. “However it has been a major problem that satellites have had trouble monitoring the very ice edge zone.”

In order to measure the thickness of a given ice layer, a radar altimeter satellite emits a radar signal and later records it being reflected back out to space. The time taken for the signal to return can be utilised to calculate the exact ice height, from which its thickness can in turn be derived.

However the topography at the edge of an ice sheet can be very steep and uneven, making it difficult for the satellite to catch the reflected signal, or know precisely from which point within the ten-kilometre signal ‘footprint’ the signal is returning from. Often the uncertainty would be too large for the results to be reliable. The practical implication was that the entire ice edge remained inaccessible for satellite monitoring.

However the science team behind CryoSat has managed to tackle this problem. Its double-antenna design means it can measure the angle of the returning signal to put an exact location on where it comes from relative to the spacecraft track. The satellite will still be able to carry out its measurements, no matter how steep the ice surface may be.

“To my mind the ice edge is the most interesting place to do science,” the Danish glaciologist states. “In the middle of the inland ice things are very stable. As climate changes, the edge is where you will be able to observe the effect first.

“American airborne measurements have shown a thinning of the Greenland glaciers by one metre per year. However our measurements on location at the ice edge show melting on an even larger scale. Now we are anxious to learn what the measurements from CryoSat will show.”

According to on-site measurements the Sermilik glacier in Southern Greenland is thinning between two and eight metres a year. Not all of this change is linked to climate change caused by human activities. The glaciologist compares the inland ice to dough for making a loaf of bread laid out on a kitchen table: “You see a slow movement from the middle towards the edge. In the case of the inland ice it may take thousands of years from a snow flake falls in the centre until it reaches the edge.

“You might say that the system has a certain built-in memory. Some of the melting we witness now is actually an aftermath of the last, mini Ice Age which ended in the last half of the 19th century”.

Systematic monitoring of air temperature has taken place since 1875. Comparing the temperature levels with the actual melting one can determine that about half of the melting is linked to changes in climate. The other half will then have other causes – primarily the aftermath of the last Ice Age.

The Danish ice monitoring effort has found thinning of large areas of the inland ice. That goes for practically the entire ice edge zone. One interesting twist to the story is that in some areas thinning is taking place despite a drop in mean temperatures.

“This goes to show the complexity of the system,” Bøggild adds. “Normally one would use the number of days with temperatures above zero degrees as an indicator of melting. Generally these two factors would be linked. However factors other than temperature may also be influencing melting. One of them is the amount of incoming solar radiation. This would make it possible to see these kind of surprising results locally”.

Despite his great expectations for CryoSat, Carl Egede Bøggild underlines that satellites will not replace ground measurements: “Satellites will give us a far more accurate view of the amount of melting but they will not tell us why the melting is taking place. In order to improve your understanding of the causes you have to do research on site. Also we will have to keep on doing measurements on site in order to verify the findings of the satellites. We are talking about two different kinds of tools supplementing each other very well.”

Original press release: CryoSat: the ice edge holds the key (ESA)

Today, scientists estimate that between one-third and one-half of our planet’s land surfaces have been transformed by human development.

A MODIS image revealing the widespread deforestation, light green and brownish areas, taking place near Mato Grosso, Brazil.

Image: Deforestation by Satellite: This image, taken April 21, 2002 by the Moderate-resolution Imaging Spectroradiometer (MODIS) flying aboard NASA’s Terra satellite reveals the widespread deforestation (light green and brownish areas) taking place near Mato Grosso, Brazil. Red dots show the locations of actively burning fires. Credit: NASA/MODIS Land Rapid Response Team

Now, a new study is offering insight into the long-term impacts of these changes, particularly the effects of large-scale deforestation in tropical regions on the global climate. Researchers from Duke University, Durham, N.C., analyzed multiple years of data using the NASA Goddard Institute for Space Studies General Circulation Computer Model (GCM) and Global Precipitation Climatology Project (GPCP) to produce several climate simulations. Their research found that deforestation in different areas of the globe affects rainfall patterns over a considerable region.

Deforestation in the Amazon region of South America (Amazonia) influences rainfall from Mexico to Texas and in the Gulf of Mexico. Similarly, deforesting lands in Central Africa affects precipitation in the upper and lower U.S Midwest, while deforestation in Southeast Asia was found to alter rainfall in China and the Balkan Peninsula. It is important to note that such changes primarily occur in certain seasons and that the combination of deforestation in these areas enhances rain in one region while reducing it in another.

This finding contradicts earlier research suggesting deforestation would result in a reduction in precipitation and increase in temperature in the Amazon basin, but carry no detectable impact on the global water cycle.

“Our study carried somewhat surprising results, showing that although the major impact of deforestation on precipitation is found in and near the deforested regions, it also has a strong influence on rainfall in the mid and even high latitudes,” said Roni Avissar, lead author of the study, published in the April 2005 issue of the Journal of Hydrometeorology.

Specifically, deforestation of Amazonia was found to severely reduce rainfall in the Gulf of Mexico, Texas, and northern Mexico during the spring and summer seasons when water is crucial for agricultural productivity. Deforestation of Central Africa has a similar effect, causing a significant precipitation decrease in the lower U.S Midwest during the spring and summer and in the upper U.S. Midwest in winter and spring. Deforestation in Southeast Asia alters rainfall in China and the Balkan Peninsula most significantly.

Elimination of any of these tropical forests, Amazonia, Central Africa or Southeast Asia, considerably enhances rainfall in the southern tip of the Arabian Peninsula. However, the combined effect of deforestation in all three regions shifts the greatest precipitation decline in the U.S. to California during the winter season and further increases rainfall in the southern tip of the Arabian Peninsula.

Improved understanding of tropical forested regions is valuable to scientists because of their strong influence on the global climate. The Amazon Basin literally drives weather systems around the world. The tropics receive two-thirds of the world’s rainfall, and when it rains, water changes from liquid to vapor and back again, storing and releasing heat energy in the process. With so much rainfall, an incredible amount of heat is released into the atmosphere - making the tropics the Earth’s primary source of heat redistribution.

“Deforestation does not appear to modify the global average of precipitation, but it changes precipitation patterns and distributions by affecting the amount of both sensible heat and that released into the atmosphere when water vapor condenses, called latent heat,” said Avissar. “Associated changes in air pressure distribution shift the typical global circulation patterns, sending storm systems off their typical paths.” And, because of the Amazon’s location, any sort of weather hiccup from the area could signal serious changes for the rest of the world like droughts and severe storms.

Clearly, land-cover changes in tropical regions carry potentially significant consequences on water resources, wildfire frequency, agriculture and related activities at various remote locations. And while greenhouse gas emissions and pollutants receive considerable attention, this study shows that land-cover change is another important parameter that needs to be considered in climate policies, especially since deforestation rates in tropical Africa, Southeast Asia, and South America have remained constant or have increased over the past two decades. Land-cover change, depending on its nature, can either mitigate or exacerbate greenhouse warming.

The researchers caution that their results are based on numerical simulations performed with a single general circulation model and that reproducing the experiment with other computer models using different atmospheric variables would be beneficial. Current research is attempting to answer why deforestation has such a major influence on precipitation patterns during respective seasons.

Original press release: Tropical Deforestation Affects Rainfall in the U.S. and Around the Globe (NASA)

The United Nations Environment Programme (UNEP) and governments around the world are preparing to celebrate two key milestones on the road to recovery for the world’s stratospheric ozone layer: the Montreal Protocol and the Vienna Convention.

“The campaign to protect the ozone layer represents an extraordinary success story – but until emissions of CFCs and other ozone-depleting substances are reduced to zero, saving the ozone layer will remain an unfinished business,” said UNEP Executive Director Klaus Toepfer.

This year’s Ozone Day theme is “Act Ozone Friendly – Stay Sun Safe”. Although levels of ozone depleting substances in the stratosphere now seem to be at or near their peak, the ozone layer will remain particularly vulnerable during the next decade or so. People must therefore be reminded to protect themselves and their children against the increased ultraviolet radiation reaching the Earth’s surface, which can cause skin cancer, cataracts and other illnesses.

The signing of the Vienna Convention for the Protection of the Ozone Layer on March 1985 when nations agreed in principle to tackle a global environmental problem will be marked in Vienna by two events. On 19 September, a seminar in Vienna on ozone science, negotiations, technologies and funding will feature Nobel Laureate Mario Molina, former UNEP Executive Director Mustafa Tolba, and former Multilateral Fund Chief Officer Omar El-Arini.

On 21 September the Government of Austria will host an awards ceremony recognizing the contributions of diplomats and scientists who contributed to the Vienna Convention’s development. Mr. Toepfer and World Meteorological Organization Secretary-General Michel Jarraud will present the awards.

The signing of the Montreal Protocol on Substances that Deplete the Ozone Layer on 16 September 1987, now celebrated every year as the International Day for the Preservation of the Ozone Layer, will be marked around the world. The Protocol builds on the general framework set out in the Convention by elaborating detailed phase-out schedules for CFCs and other ozone-depleting substances.

Celebrations of International Ozone Day are being organized by governments worldwide, for example:

• Mexico has organized an event to mark the closure of the Quimobasicos CFC production facilities, the largest manufacturer of CFCs in Latin America. This historic closure results in the total elimination of the country’s CFC production, the reduction of Latin America’s production to 60 percent, and the dropping of global output by 12 to 13 percent
• China’s celebration in Shenzen city will focus on ozone protection in cities and towns.
• The United States is celebrating using this year’s theme with a ” Sun Safety Summit for Skin Cancer Prevention” co-hosted by the US Environmental protection Agency, the Center for Disease Prevention and the National Council on Skin Cancer prevention.
• The French Ministry of Ecology and Development will organize a seminar in Paris on “Ozone, Climate Change and Mobility” that will be open to the public and will feature leading international experts.
• In Mauritius, the Minister of Environment & National Development and the Minister of Information Technology together with UNEP will host a press conference where a new UNEP educational web site for children will have its global launch (www.ozzyozone.org).
• Indonesia is organizing a Regional Ozone Day for South-East Asia and the Pacific, involving celebrations with the Diplomatic Corps from the respective countries.

The private sector is also getting into the action. For example, India’s largest international carrier, Air India, and one of the country’s leading banks, the Bank of Maharashta, are hosting outreach events and producing awareness materials.

In addition, UNEP’s OzonAction Programme, which provides technical and training services to assist developing countries with meeting their compliance commitments under the Protocol, is supporting this year’s celebrations through:

• Two new 30-second radio spots reinforcing the message of the “Ozzy Ozone” story are being distributed around the world in English, French, Portuguese and Spanish.
• Three new short public service television announcements are being distributed around the world in English, French and Spanish: “Ozzy and Isabella”, “Buy Ozone Friendly Products” and a short advertisement on the “Ozzy Ozone” video.
• Airlines that travel close to the stratosphere have been encouraged to show UNEP’s Ozzy Ozone video as part of in-flight entertainment; so far Air India, British West Indies Airline and Air Mauritius have agreed to show the video during September. (In addition, Air India has produced a special issue of its in-flight magazine “Namsakaar” on ozone layer protection with the potential for reaching some one million passengers.)
• A new cartoon booklet for children featuring the Ozzy Ozone character, “Ozzy Ozone, Defender of Our Planet”. The booklet is suitable for distribution in schools and will be available in Arabic, Chinese, English, French, Japanese, Portuguese, Russian, and Spanish

Original press release: Two Decades of Protecting the Ozone Layer to be Marked (UNEP)

Friday (16 September) is International Day for the Preservation of the Ozone Layer. This year scientists at British Antarctic Survey (BAS) commemorate their discovery of the Antarctic ‘ozone hole’ 20 years ago and commend the historic international agreement (the Montreal Protocol 1987) that will lead to its eventual recovery.

Jonathan Shanklin, one of the researchers who made the discovery says,

“The 2005 hole is larger and deeper than the holes that formed when the discovery was made but the situation would be much worse if the Montreal Protocol had not come into force. This agreement shows us that global action by governments to stop the release of ozone depleting chemicals really can help society to successfully mitigate a global environmental problem. We are still experiencing large losses of Antarctic ozone each spring because CFCs and other chemicals live for a long time in our atmosphere. However, the ban ensures that we will see an improvement in the future. We now need to take similar actions to control greenhouse gasses, otherwise we will bequeath future generations a significantly different climate from that of today.”

Covering an area of around 22 million square kilometres this year’s hole is a little smaller than the record-breaking event in August 2003. Measurements made during August and September at BAS Halley and Rothera Research Stations reveal a 50% reduction on normal ozone levels over the base of the Antarctic Peninsula and the Weddell Sea, and a 20% reduction over the tip of South America and the Falkland Islands. The increased ultra violet light reaching the surface poses a medical hazard to people living under the ‘hole’ and without suitable protection people face the prospect of rapid sunburn and potentially more serious skin damage.

Original press release: 20th Anniversary of ozone hole discovery – International Ozone Day (BAS)

Two NASA satellites, planned for launch no earlier than Oct. 26, will give us a unique view of Earth’s atmosphere. CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) are undergoing final preparations for launch from Vandenberg Air Force Base, Calif.

CloudSat and CALIPSO will provide a new, 3-D perspective on Earth’s clouds and airborne particles called aerosols. The satellites will answer questions about how clouds and aerosols form, evolve and affect water supply, climate, weather and air quality.

CloudSat and CALIPSO employ revolutionary tools that will probe Earth’s atmosphere. Each spacecraft carries an “active” instrument that transmits pulses of energy and measures the portion of the pulses scattered back to the instrument.

CloudSat’s cloud-profiling radar is more than 1,000 times more sensitive than typical weather radar. It can detect clouds and distinguish between cloud particles and precipitation. “The new information from CloudSat will answer basic questions about how rain and snow are produced by clouds, how rain and snow are distributed worldwide and how clouds affect the Earth’s climate,” said Dr. Graeme Stephens, CloudSat principal investigator at Colorado State University, Fort Collins, Colo.

CALIPSO’s polarization lidar instrument can detect aerosol particles and can distinguish between aerosol and cloud particles. “With the high resolution observation that CALIPSO will provide, we will get a better understanding of aerosol transport and how our climate system works,” said Dr. David Winker, CALIPSO principal investigator at NASA’s Langley Research Center, Hampton, Va.

The satellites will be launched into a 438-mile circular, sun-synchronous polar orbit, where they will fly in formation just 15 seconds apart as members of NASA’s “A-Train” constellation with three other Earth Observing System satellites. The A-Train includes NASA’s Aqua and Aura satellites and France’s PARASOL satellite.

The usefulness of data from CloudSat, CALIPSO and the other A-Train satellites will be much greater when combined. The combined set of measurements will provide new insight into the global distribution and evolution of clouds that will lead to improvements in weather forecasting and climate prediction.

CloudSat is managed by NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif. The radar instrument was developed at JPL, with hardware contributions from the Canadian Space Agency. Colorado State University provides scientific leadership and science data processing and distribution.

Other contributions include resources from the U.S. Air Force and the U.S. Department of Energy. Ball Aerospace and Technologies Corp. designed and built the spacecraft. A host of U.S. and international universities and research centers provides support to the science team. Some of these activities are contributed as partnerships with the project.

CALIPSO was developed through collaboration between NASA and the French Space Agency, Centre National d’Etudes Spatiales (CNES). NASA’s Langley Research Center leads the CALIPSO mission and provides science team leadership, systems engineering, payload mission operations, and validation, processing and archiving of data. Langley also developed the lidar instrument in collaboration with the Ball Aerospace and Technologies Corp., which developed the onboard visible camera.

NASA’s Goddard Space Flight Center, Greenbelt, Md., provides project management, system engineering support and overall program management. CNES provides a PROTEUS spacecraft developed by Alcatel, the imaging infrared radiometer, payload-to-spacecraft integration and spacecraft mission operations. The Institut Pierre Simon Laplace in Paris provides the imaging infrared radiometer science oversight, data validation and archival. Hampton University provides scientific contributions and manages the outreach program.

Original press release: NASA Satellites Will Reveal Secrets of Clouds and Aerosols (NASA)