Warming Climate: Consensus or Controversy

Spurred by a warming climate, daily record high temperatures occurred twice as often as record lows over the last decade across the continental United States, new NCAR research shows, while author of “The Rough Guide to Climate Change” Bob Henson gets ready for Copenhagen and David Hosansky asks “Which makes the news? Consensus or controversy”.

BOULDER—Spurred by a warming climate, daily record high temperatures occurred twice as often as record lows over the last decade across the continental United States, new research shows. The ratio of record highs to lows is likely to increase dramatically in coming decades if emissions of greenhouse gases continue to climb.

“Climate change is making itself felt in terms of day-to-day weather in the United States,” says Gerald Meehl, the lead author and a senior scientist at the National Center for Atmospheric Research (NCAR). “The ways these records are being broken show how our climate is already shifting.”

This graphic shows the ratio of record daily highs to record daily lows observed at about 1,800 weather stations in the 48 contiguous United States from January 1950 through September 2009. Each bar shows the proportion of record highs (red) to record lows (blue) for each decade. The 1960s and 1970s saw slightly more record daily lows than highs, but in the last 30 years record highs have increasingly predominated, with the ratio now about two-to-one for the 48 states as a whole.

The study, by authors at NCAR, Climate Central, The Weather Channel, and the National Oceanic and Atmospheric Administration (NOAA), has been accepted for publication in Geophysical Research Letters. It was funded by the National Science Foundation, NCAR’s sponsor, the Department of Energy, and Climate Central.

If temperatures were not warming, the number of record daily highs and lows being set each year would be approximately even. Instead, for the period from January 1, 2000, to September 30, 2009, the continental United States set 291,237 record highs and 142,420 record lows, as the country experienced unusually mild winter weather and intense summer heat waves.

A record daily high means that temperatures were warmer on a given day than on that same date throughout a weather station’s history. The authors used a quality control process to ensure the reliability of data from thousands of weather stations across the country, while looking at data over the past six decades to capture longer-term trends.

This decade’s warming was more pronounced in the western United States, where the ratio was more than two to one, than in the eastern United States, where the ratio was about one-and-a-half to one.

The study also found that the two-to-one ratio across the country as a whole could be attributed more to a comparatively small number of record lows than to a large number of record highs. This indicates that much of the nation’s warming is occurring at night, when temperatures are dipping less often to record lows. This finding is consistent with years of climate model research showing that higher overnight lows should be expected with climate change.

More records ahead

In addition to surveying actual temperatures in recent decades, Meehl and his co-authors turned to a sophisticated computer model of global climate to determine how record high and low temperatures are likely to change during the course of this century.

The modeling results indicate that if nations continue to increase their emissions of greenhouse gases in a “business as usual” scenario, the U.S. ratio of daily record high to record low temperatures would increase to about 20-to-1 by mid-century and 50-to-1 by 2100. The mid-century ratio could be much higher if emissions rose at an even greater pace, or it could be about 8-to-1 if emissions were reduced significantly, the model showed.

The authors caution that such predictions are, by their nature, inexact. Climate models are not designed to capture record daily highs and lows with precision, and it remains impossible to know future human actions that will determine the level of future greenhouse gas emissions. The model used for the study, the NCAR-based Community Climate System Model, correctly captured the trend toward warmer average temperatures and the greater warming in the West, but overstated the ratio of record highs to record lows in recent years.

However, the model results are important because they show that, in all likely scenarios of future greenhouse gas emissions, record daily highs should increasingly outpace record lows over time.

“If the climate weren’t changing, you would expect the number of temperature records to diminish significantly over time,” says Claudia Tebaldi, a statistician with Climate Central who is one of the paper’s co-authors. “As you measure the high and low daily temperatures each year, it normally becomes more difficult to break a record after a number of years. But as the average temperatures continue to rise this century, we will keep setting more record highs.”

An expanding ratio

The study team focused on weather stations that have been operating since 1950. They found that the ratio of record daily high to record daily low temperatures slightly exceeded one to one in the 1950s, dipped below that level in the 1960s and 1970s, and has risen since the 1980s. The results reflect changes in U.S. average temperatures, which rose in the 1950s, stabilized in the 1960s, and then began a warming trend in the late 1970s.

Even in the first nine months of this year, when the United States cooled somewhat after a string of unusually warm years, the ratio of record daily high to record daily low temperatures was more than three to two.

Despite the increasing number of record highs, there will still be occasional periods of record cold, Meehl notes.

“One of the messages of this study is that you still get cold days,” Meehl says. “Winter still comes. Even in a much warmer climate, we’re setting record low minimum temperatures on a few days each year. But the odds are shifting so there’s a much better chance of daily record highs instead of lows.”

Millions of readings from weather stations across the country

The study team analyzed several million daily high and low temperature readings taken over the span of six decades at about 1,800 weather stations across the country, thereby ensuring ample data for statistically significant results. The readings, collected at the National Oceanic and Atmospheric Administration’s National Climatic Data Center, undergo a quality control process at the data center that looks for such potential problems as missing data as well as inconsistent readings caused by changes in thermometers, station locations, or other factors.

Meehl and his colleagues then used temperature simulations from the Community Climate System Model to compute daily record highs and lows under current and future atmospheric concentrations of greenhouse gases.

Consensus and controversy: Which makes the news?

David Hosansky  (24 November 2009):  

This has been quite a banner year for climate skeptics. Even though reports continue to pour in about melting glaciers, sea ice loss, and temperatures across much of the globe remaining unusually warm, fewer and fewer Americans seem to believe the climate is warming.

In the spring of 2008, a poll by the Pew Research Center for the People & the Press found that 71% of Americans believed there was solid evidence that the average temperature on Earth has been getting warmer. As of last month, that number had dropped to 57%. Similarly, a Gallup poll in March found that 41% of Americans felt that the seriousness of global warming was being exaggerated—the highest level of skepticism in more than a decade of Gallup polling on this subject. Similar drops in concern appear in a poll released just today by ABC and the Washington post.

Last week’s news about the hacking of some 1,000 private e-mails written by prominent climate scientists, including Kevin Trenberth here at NCAR, is likely to further embolden skeptics. Some say the e-mails paint a picture of scientists who were distorting climate change research—an allegation sharply denied by the hacking target, the University of East Anglia’s Climatic Research Unit (CRU).

The media coverage of the e-mail hacking is a discouraging reminder of how hard it is to inform Americans about climate change. In the first three days after the hacking incident was initially reported, the coverage generated about 1,500 hits on Google News. That’s an enormous level of media interest for a subject like climate change. By comparison, an NCAR news release is lucky to generate 300 to 400 media hits as measured by Google News, and then only when the research has major societal implications, such as a recent study linking climate change to lower water levels in some of the world’s major rivers.

With news organizations cutting back on their science coverage, they don’t have the resources to cover new research. They’re looking for controversies like the hacking of e-mails. So when scientists are in agreement over global warming, that doesn’t generate news because it’s not controversial. When 18 of the nation’s most prominent scientific organizations wrote to Congress last month about the broad scientific consensus over global warming, major news organizations didn’t do any stories at all.

As a former reporter, I’m not trying to make the case that the hacking of e-mails wasn’t a legitimate news story. But it would be nice if that were better balanced with stories about the scientific consensus.

There are many reasons that Americans remain uncertain about the validity of global warming, years after virtually all climate scientists considered the case proven. Temperatures in much of the United States aren’t rising as rapidly as elsewhere in the world. Heat waves don’t generate the kind of angst that a snowstorm might cause. And the economy could be making many in the public uneasy about the sacrifices that could be involved in cutting emissions.

But the coverage of the hacking at CRU reveals another reason. Mainstream news media, sadly, are simply not driven to cover the science of global warming. If the traditional motto of journalism is “just the facts,” perhaps the motto in this 24-hour, point-counterpoint news culture should be: “just the disputes over the facts.”

 Now comes the hard part

Bob Henson (18 November 2009):   

What happens in Copenhagen, Denmark, from 7 to 18 December could affect our lives for years to come. Diplomats from almost 200 countries will huddle, confer, cajole, and eventually forge the structure of a new global agreement to reduce carbon emissions.

The Copenhagen meeting will take place at the city’s Bella Center, where a windmill serves as literal and symbolic evidence of Denmark’s commitment to alternative energy.

The Copenhagen meeting—technically, the 15th Conference of the Parties (COP15) to the United Nations Framework Convention on Climate Change (UNFCCC)—has been dubbed many things, including the last chance to save our planet. Any gathering would have trouble living up to such hype, and in fact, expectations are already getting tamped down. Leaders from the United States, China, and other Asia-Pacific nations announced on 15 November that a binding agreement on emissions would be impossible to achieve in Copenhagen. Instead, they’ll seek a “political agreement” that might lead to a binding deal in 2010.

Though widely expected, this pullback was sobering enough to prod the London Telegraph to ask its readers, “Has the battle against climate change been lost?”

The obituary may be premature: much still rides on the Copenhagen meeting. Many issues remain on the table, including how to structure carbon trading and how to help developing nations adapt to climate change already in the works.

Along with the diplomatic talks, there will be hundreds of side events involving thousands of scientists, activists, journalists, and legislators, including some 200 U.S. senators and representatives.

A handful of people from UCAR and NCAR will be in the mix as well. We’re each attending for various reasons—to present research results, share educational resources, meet international peers, and more— but all of us are keenly interested in sharing our knowledge and learning more about climate change and the tremendous challenge the world faces in responding to it.

We’ll be posting updates here on NOTES FROM COPENHAGEN as our schedules allow, beginning in earnest around 11 December and continuing through the end of the meeting. You can also follow our updates via RSS news feed, Twitter, or Facebook.

Source: www.ucar.edu