Tag Archives: temperature

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

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. 

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