Tag Archives: climate change

The New Climate Dice

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During the extreme heat waves and droughts of the early 1980s, climatologist James Hansen noticed coincident public discussions about the possible link of extreme events to climate change. He says discussion cooled, however, when natural variability turned up a season with average or cold temperatures. In 1988, another heat wave and drought wiped out crops in the U.S. Midwest, and resulted in more than 5,000 deaths, according to NOAA’s National Climatic Data Center. That same year, Hansen introduced the analogy of loaded dice to demonstrate variability and the growing frequency of extreme temperature events.

On one of the six-sided dice, Hansen painted two sides blue, two sides white, and two sides red to represent the chance of a cold, average, or warm summer season, respectively. That’s how the dice would have rolled from 1951 to 1980, when climate was relatively stable. On the other die – this one loaded – Hansen painted one side blue, one side white, and four sides red. That’s how climate models suggested the dice would roll by the first decade of the 21st century, should the increase of greenhouse gases in the atmosphere play out as it did.

“If you keep track for several seasons you notice the frequency of the anomalies has now changed, and you’re getting much more of those on the warm side than on the cool side,” Hansen says.

The changes that Hansen and colleagues calculated in 1988 turned out to be close to reality, as far as how many sides of the dice would now be red as opposed to blue to represent today’s climate. But a key difference between the 1988 dice and the new climate dice is the addition of an entirely new color. Almost one full side previously red is now brown, representing a new category of extreme hot events.

“I didn’t think about adding another color in 1988,” Hansen says. “Since then I have realized that the extreme cases are the most interesting and hold the most potential for impact, such as we’re seeing this summer in the case of the drought and devastated corn crop.”

The division between warm and cool will continue to change in the future, Hansen says. “But it’s still a crapshoot and you shouldn’t take one cool season as an indication that there’s something wrong with our understanding of global temperature and warming.”

Hansen and colleagues continue to use the dice for communication purposes, but they now employ a different statistical tool – the bell curve – that they say better demonstrates the change in temperature anomalies, particularly at the extremes.

Text by Kathryn Hansen. Top image: James Hansen of NASA’s Goddard Institute for Space Studies. Credit: NASA

AGU2011: How Shifting Storm Tracks Are Amplifying Climate Change

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Tropical cyclones and hurricanes generate the most headlines, but it’s mid-latitude storms churning through heavily populated parts of North America, Europe, and Asia that make the weather most of us actually experience.

Climate models predict that these mid-latitude storms should shift poleward and that the intensity and frequency of the storms could change as global temperatures rise, but actual evidence of such a shift has been difficult to pin down. However, a recently published analysis of 25 years of cloud data captured by satellites offers a compelling piece of evidence that suggests storm tracks are indeed shifting.

The research, led by (former) Scripps Institute of Oceanography scientist Frida Bender, shows that storms tracks have shifted poleward, narrowed, and grown less cloudy since 1983, particularly in the Southern Hemisphere. The analysis, based on data from the International Satellite Cloud Climatology Project, finds that storm tracks have shifted by about 0.4 degrees over the last 25 years.

What’s more, the analysis suggests that changes in the location and intensity of storms could amplify global warming. The researchers detected what amounts to a 2 percent decline in storm tracks over the 25 year record. The decline in cloudiness is of particular importance because it suggests that intensity of storms is likely decreasing. And since clouds reflect large amounts of sunlight, reduced cloudiness means that ocean surfaces beneath storm systems are likely growing warmer.

Graeme Stephens, the director of NASA’s Center for Climate Science at the Jet Propulsion Laboratory, underscored the importance of the study in a piece published by Nature Climate Change noting:

Bender and colleagues’ study reminds us of the importance of changes in the large-scale clouds associated with frontal storms in storm-track regions. Not only do the polewards shifts in storm-track location profoundly affect precipitation patterns in mid-latitude regions, but associated changes in cloudiness also exert a significant positive feedback on global warming.

Text by Adam Voiland. Frida Bender presented a poster about the topic  at an American Geophysical Union Meeting on Dec. 6, 2011. The full paper is available here. Video of Midwest tropical storm originally published by NASA’s Earth Observatory. 

To What Degree is Extreme Weather Linked to Climate Change?

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As flood waters continue to inundate Thailand and drought parches Texas, the Intergovernmental Panel on Climate Change and Goddard Institute for Space Studies Director James Hansen have both released new statements about the connection between extreme weather and climate change. Although linking extreme weather to climate change has generated controversy in the past, both of the new reports point plainly to a connection.The IPCC, an international organizational that represents the scientific consensus of hundreds of leading climatologists, put it this way in the executive summary of its new report.

It is very likely that there has been an overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights, on the global scale, i.e., for most land areas with sufficient data. It is likely that these changes have also occurred at the continental scale in North America, Europe, and Australia.There have been statistically significant trends in the number of heavy precipitation events in some regions. It is likely that more of these regions have experienced increases than decreases, although there are strong regional and subregional variations in these trends.

There is medium confidence that some regions of the world have experienced more intense and longer droughts, in particular in southern Europe and West Africa, but in some regions droughts have become less frequent, less intense, or shorter, e.g., in central North America and northwestern Australia.There is evidence that some extremes have changed as a result of anthropogenic influences, including increases in atmospheric concentrations of greenhouse gases. It is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures on the global scale. There is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation on the global scale.

There is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at regional scales because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes.

Meanwhile, Hansen has released the draft of a new paper (pdf) that also tackles the topic of extreme weather and climate. He’s somewhat less equivocal in his summary of the state of the science:

The “climate dice” describing the chance of an unusually warm or cool season, relative to the climatology of 1951-1980, have progressively become more “loaded” during the past 30 years, coincident with increased global warming. The most dramatic and important change of the climate dice is the appearance of a new category of extreme climate outliers. These extremes were practically absent in the period of climatology, covering much less than 1% of Earth’s surface. Now summertime extremely hot outliers, more than three standard deviations (σ) warmer than climatology, typically cover about 10% of the land area. Thus there is no need to equivocate about the summer heat waves in Texas in 2011 and Moscow in 2010, which exceeded 3σ – it is nearly certain that they would not have occurred in the absence of global warming. If global warming is not slowed from its current pace, by mid-century 3σ events will be the new norm and 5σ events will be common.

Text by Adam Voiland. Lead image of flooding in Ayutthaya published originally by NASA’s Earth Observatory. Extreme weather curves published originally by the IPCC. Land trends over land published originally on James Hansen’s Columbia University website. 

See This Year's Arctic Sea Ice Minimum

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The National Snow and Ice Data Center (NSIDC) has tentatively announced that Arctic sea ice has reached its minimum extent for the year. From the NSIDC release:

The blanket of sea ice that floats on the Arctic Ocean appears to have reached its lowest extent for the year. Arctic sea ice extent fell to 4.33 million square kilometers (1.67 million square miles) on September 9, 2011. This year’s minimum was the second lowest in the satellite record, which started in 1979. The lowest extent was recorded in 2007.Over the last thirty years, ice extent, a two-dimensional measure of the ice cover on the Arctic Ocean, has declined in all months, with a more pronounced drop in summer. Scientists attribute this decline in large part to climate change. Arctic sea ice melts and refreezes in an annual cycle, reaching its lowest point in late summer, and its highest point in late winter.

Meanwhile, NASA Goddard Space Flight Center has posted HD video of the decline from the near maximum ice extent in early spring of 2011 through Sept. 9, 2011. The visualization (above) is based on data collected by Aqua’s AMSR-E instrument. From Goddard’s Flickr caption:

Sea ice goes through this shrink-and-swellrhythm every year, but since consistent satellite observations began in1979, both the annual minimum at the end of summer and the annualmaximum at the end of winter continue to decline in area and thickness.Consistent with rising temperatures globally and specifically in theArctic, climate scientists are concerned with this trend both as anindicator of climate change and as a feedback mechanism. As the white,highly reflective ice disappears, darker ocean waters appear. Thisdarker surface absorbs more solar radiation and acts as a positivefeedback to the warming that is already occurring and causing the changein the first place.

On Sept. 20th, NASA’s Cryosphere Program Manager, Tom Wagner, shared his take on Arctic sea ice with television audiences across the country.

Text by Adam Voiland. Visualization by the Scientific Visualization Studio based at Goddard Space Flight Center.

Have the Last Four Summers and Winters Felt Warmer?

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During a congressional hearing in 1988, Goddard Institute for Space Studies climatologist James Hansen predicted that a perceptive person would be able to notice the climate was changing by the early 21st century. Has his prediction panned out? He digs into the topic in a discussion published this week on his website.

The short answer: yes, depending on where you live, you should be able to tell that in the last four years, for example, summers have been warmer than average. The last four winters have also been noticeably mild in most parts of the world. (Though it’s worth noting that the last two winters in the continental United States have actually been cooler than average).

Read on below to see how Hansen explains it in more detail. (I’ve excerpted some of the more accessible sections of the text and two graphs, but the full discussion is available here as a pdf.)  More context and details about trends in the global surface temperature record are also available.

This past winter, for the second year in a row, seemed pretty extreme in both Europe and the United States. So this is a good time to check quantitatively how seasonal climate change is stacking up against expectations.

People’s perception of climate change may be the most important factor determining their willingness to accept the scientific conclusion that humans are causing global warming (or global climate disruption, as you please). Itis hard to persuade people that they have lying eyes.

In the paperattached to my congressional testimony in 1988 (1) we asserted that theperceptive person would notice that climate was changing by the early21st century. Now we can check the degree to which the real world has lived up to this expectation. The answer will vary from one place to another, so let’s make a global map for this past winter. Each gridbox will be colored red, white or blue, depending on how the local temperature this past winter compared with the categories established by the 1951-1980 climatology.

Figure 7 (above) shows the result for the last four winters (summers in the Southern Hemisphere). To make the maps even more useful we use dark blue and dark red to show those places in which the temperature fell in the extreme (>2 standard deviations) category that occurred only a few percent of the time in the period of climatology1. The extreme cases are important because those are the ones that have greatest practical implications, especially for nature. Species are adapted to climate of the past, so a change to more extreme climates can be detrimental, especially if it occurs so rapidly that species cannot migrate to stay within tolerable climatic conditions.

The numbers on the top of the maps are the percent of the area falling in the five categories: very cold, cold, normal, hot, very hot. In the period of climatology those numbers averaged 2%, 31%, 33%, 31%, 2%, rounded to the nearest percent.

Figure 7 reveals, for example, that the past two winters in Northern Europe both fell in the category of “cold” winters, but not extreme cold. The area hot or very hot (51-73%) far exceeded the area with cold or very cold conditions in all four years (14-27%).

Figure 8 (top) shows results for Jun-Jul-Aug for each of the past four years. In both Jun-Jul- Aug and Dec-Jan-Feb it is apparent that the area falling in either the hot or very hot category totals 64-78% in agreement with our 1988 climate simulations.

The perceptive person who is old enough should be able to recognize that the frequency of unusually mild winters is now much greater than it was in the period 1951-1980. But mild winters may not have much practical impact. So a return to one or two colder than average winters may affect the public’s perception of climate change.

On the other hand, the huge increase in the area with extremely hot summers, from 2-3% in 1951-1980 to as much as 30-40 percent in recent years and most of the land area in 2010. If people cannot recognize that summers are becoming more extreme they may need to have their senses examined or their memories. Perhaps the people who do not recognize climate change are living in air-conditioned environments, which are restricted mainly to one species.

–Adam Voiland, NASA’s Earth Science News Team

You're Getting Warmer

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Have you noticed all the hot – and erratic – weather this summer?

So has NASA GISS climatologist Jim Hansen. He’s out with the draft of a new paper and popular summary that explores July’s anomalous weather. His main point:

The global average July 2010 temperature was 0.55°C warmer than climatology in the GISS analysis, which puts 2010 in practically a three way tie for third warmest July. July 1998 was the warmest in the GISS analysis, at 0.68°C.

Here’s his prediction on whether 2010 will shape up as the warmest in the GISS record:

2010 is likely, but not certain, to be the warmest year in the GISS record. However, because of the cooling effect of La Niña in the remainder of the year, there is a strong possibility that the 2005 and 2010 global temperatures will be sufficiently close that they will be practically indistinguishable.

And his take on whether the extreme weather events – such as the brutal heat wave that’s hammered Moscow – are connected to global climate change:

The location of extreme events in any particular month depends on specific weather patterns, which are unpredictable except on short time scales. The weather patterns next summer will be different than this year. It could be a cooler than average summer in Moscow in 2011…What we can say is that global warming has an effect on the probability and intensity of extreme events.

This points to the distinction that scientists are always making between weather and climate. Solar activity, El Nino or even volcanic eruptions can affect the weather and temperature over a short term. But when it comes to classifying what is happening to the climate, the trend must be clear and free of these influences. The climate “signal” must emerge from the data over the course of at least a decade.

What’s happening with the global surface temperature record fits this bill, Hansen said in the draft paper. Despite El Ninos, La Ninas, changes in the Arctic Oscillation, fluctuations in the sun’s radiance, snowy winters and cool summers, hot summers and warm winters, the continued trend of the average global surface temperature remains on an upward climb.

To learn more about NASA’s surface temperature record, visit this temperature update from earlier this year. Also, you can visit GISS’s technical page for detailed information about GISS’s surface temperature record.

— By Patrick Lynch and Adam Voiland, NASA’s Earth Science News Team

–The map at top was created by NASA’s Earth Observatory using data from MODIS 

Puzzling Over the Pieces

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Guest contributor Karen Romano Young (photo at right) blogs from NASA’s ICESCAPE expedition…

There’s a sign on the door of the room I share with Sharmila Pal and Emily Peacock. It’s a green square of plastic engraved with a picture of a polar bear and the words “SCIENCE – LATE SLEEPER.” So many of the scientists aboard Coast Guard Cutter Healy for the ICESCAPE mission are awake through the night that the ship’s engraver, Chief Warrant Officer 3 Sean Lyons, has turned out a special  edition of late sleeper signs, complete with a rocket ship for NASA. Almost every door boasts a sleeper sign of one kind or another.

The reason? Aboard ICESCAPE, the science goes on 24 hours a day. We’re on a path to the far north, steaming from station to station through the night. Sometimes we’re in ice, sometimes we’re in open ocean, sometimes there’s a mix. Sometimes, there are walruses and seals. Each group of scientists has divided their schedule into shifts, so while some are catching their zzz’s behind those “late sleeper” signs, others are awake and overseeing operations, making measurements, and processing samples.

NASA’s Stanford Hooker takes the small boat out to measure light and take water samples, away from the interference of the ship. Karen Frey’s group from Clark University works on ice stations and takes Van Veen grabs in the open sea. (It’s like a giant pooper-scooper that scoops sediment from the ocean floor).

Bob Pickart of the Woods Hole Oceanographic Institution works to assess currents and other elements of physical oceanography, such as eddies and upwelling, as we pass through the ocean. James Swift, from Scripps Institution of Oceanography, oversees the CTD, a rosette of siphons and bottles triggered to sample water at various depths. (CTD stands for conductivity, temperature, and depth.) Greg Mitchell, Rick Reynolds, and their groups from Scripps measure the ocean’s optical properties with a small profiler dropped from the bow and with the Inherent Optical Properties (IOP) package of instruments deployed from the stern.

Sketch by Karen Romano Young

“We’re all working on different pieces of the same puzzle,” Reynolds says. “It’s impossible for one group to measure all we need to know. [Chief Scientist] Kevin Arrigo’s group is looking at core pigments, the plant pigments in the water column. Others are looking at chemical analyses of the nutrients in the water. It’s a big team effort. The ice people are working in a completely different environment, but there are algae in both places.”

The $250,000 IOP suite of instruments assesses the health of the ocean by analyzing the absorption and scattering of light by particles suspended in the water, including chlorophyll-rich algae; the quantity and quality of algae (the health and growth rate); and the presence of minerals and sediment. Each instrument on the IOP contributes to a picture of the makeup of the particles by assessing changes in light transmission.

“We start at the top,” says Reynolds (shown at left). “We look at what the NASAsatellite sees — the sea color — and parse out the differentcharacteristics of the water — how much algae, and what else is there,such as minerals from rivers, re-suspended sediment (mud stirred intothe water) and melting ice.” The resulting data will help thescientists develop new algorithms — equations for solving problems –to support the satellites.

NASA ice- and ocean-observing satellites, now working for more than ten years, are beginning to allow us to examine changes in the climate. One purpose of ICESCAPE is to look at the ocean with greater detail than the satellites offer, in order to improve and refine the interpretation of the satellite data. 

“We’re here because NASA wants to know what the satellites are seeing right here at the stations,” says Reynolds, “where nobody else may sample for decades, because the ocean is so vast.”

All imagery, including the IOP sketch, courtesy of Karen Romano Young 

Working (Very) Remotely

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Bryan Fabbri, Fred Denn, and Bob Arduini typically drive to their jobs at NASA’s Langley Research Center in Hampton, Va. But then there are a few days each month when they take the helicopter instead.

The three scientists are part of the small, hands-on team that maintains a suite of meteorological and climate-observing instruments on the Chesapeake Light, a platform lighthouse 15 miles off the Virginia coast in the Atlantic Ocean.

The instruments record air and sea surface temperature, the amount of sunlight and heat absorbed and reflected by the ocean surface, wind speed, aerosol composition, and on and on. The measurements are made to validate the observations made by the Langley-managed Clouds and the Earth’s Radiant Energy System (CERES).

The CERES satellite instruments have been operating for more than a decade, creating a long-term record of a key driver of Earth’s climate – the balance of incoming and outgoing solar radiation known as the “energy budget.” And the instruments that Fabbri, Denn and Arduini maintain on Chesapeake Light serve to validate the observations CERES makes over the oceans. The project is called COVE (CERES Ocean Validation Experiment) and began along with CERES more than a decade ago.

In a job that usually demands a lot of time crunching data in front of a computer screen, the regular trips to the lighthouse offer a chance for something different. They also highlight a side of science that isn’t often discussed: the grunt work of making sure your instruments are working properly…or haven’t corroded in the humid salt-air…or haven’t blown off the platform with an open-ocean gust. If the sensors aren’t working properly, CERES observations over the ocean would be much more difficult to validate.

It doesn’t hurt that this important work means getting out in the middle of the ocean every now and then.

“You can’t beat that part of it,” Fabbri said. “I get a little stir crazy. I like getting out of the office and out there to work on the instruments. It doesn’t hurt to take the helicopter out.”

— By Patrick Lynch, NASA’s Langley Research Center