Don't be Fooled by Weather's Ups and Downs: The Climate is Warming -- Rapidly
Even with global temperatures flirting with the record books as the earth warms in response to higher concentrations of greenhouse gases, the weather will vary. But don't be misled by short-term and local variations. The long-term global trends persist, and the odds of below normal temperatures will rapidly diminish as global warming continues.
Some periods are cooler than others; and there are geographic variations. For example, this map of global temperature anomalies during November 2009 (red dots show areas warmer than normal, while blue dots show cooler areas) shows that while the contiguous U.S. was experiencing the 3rd warmest November on record, it was colder than normal in East Asia. However, this map of global temperature anomalies during October 2009 shows much of the contiguous U.S. and northern Europe experiencing cooler than normal conditions, while nearly all the rest of the world was above normal. While U.S. conditions were very different from month to month, global temperatures overall were well above normal both months. It is important to focus on global conditions and not just conditions in your neighborhood -- though your local weather of course is important!
Likewise, it is important to look at the long term trend when trying to understand how climate is changing. Long term changes in precipitation, temperatures and other climate variables are occurring as human activity rapidly increases the concentrations of greenhouse gases in the atmosphere. But there are other factors -- that still will cause climate variability over the near term. One such factor is what is called the El Nino - Southern Oscillation (ENSO) phenomenon in the tropical Pacific, in which surface waters can be unusually cold (known as La Nina) or warm (El Nino). ENSO conditions affect global atmospheric temperatures and weather conditions worldwide.
One year, season or month can be cooler than another. But the longer term trend over decades, centuries and even thousands of years is clear: we are warming quickly. Globally, the warmest years on record have been concentrated in the last decade.
Climate change denialists are fond of focusing attention on relatively short periods of time and limited geographic areas to raise doubts about climate change. One of their arguments focuses very specifically on record global temperatures in 1998 compared to temperatures since then. The video below exposes that disingenuous argument. It is from the "Climate Denial Crock of the Week" video series from Greenman Studio LLC, a graphic design and animation studio in Midland, Michigan. The full series of videos is available online.
One way to understand how cooler periods can occur even as the planet warms is to consider how the odds of experiencing a colder-than-normal period decline as the earth warms. NASA climate scientist Jim Hansen does this with dice. One die represents the normal conditions for 1951-1980. It has two blue sides for colder years, two red sides for warmer years and two white sides for years with relatively normal temperatures. Since there are six sides to the die, the odds of seeing any particular conditions (warmer,cooler or normal) were two chances out of six (one out of three).
The second die changes as the earth warms. According to Hansen, because of the buildup of greenhouse gases in the atmosphere, four (rather than two) sides of this die already are red. We've doubled the odds of a warmer than normal year. There is only one blue (cool) side and one white (normal) side -- so the odds of cooler or even normal years have already been cut in half, to one chance in six. We still have a chance of a year that is cooler than the 1951-1980 average, but such years are much less likely.
When might we have to add another red side? Hansen suggests we may have to do that within the next 10 or 15 years. The odds of a warmer than normal year then would be 5 out of 6 with the die; while the odds of a normal or cooler than normal year would be reduced to less than 1 out of 6.
See Hansen explain this in the video below where he responds to questions from New York Times journalist Andy Revkin in this inverview from June 2008.
Recent WWF blog postings:
- NASA: November was the Warmest on Record (15 Dec 2009)
- U.K. Met Office: 2010 Likely to be Warmest on Record (11 Dec 2009)
- World Meteorological Organization: 2009 Among Top Ten Warmest Years on Record (11 Dec 2009)
- UK Met Office: This Decade is Warmest on Record (8 Dec 2009)
Other Online Resources:
- A Warming Pause? RealClimate, 6 October 2009
- Climate Myths: Global Warming Stopped in 1998. New Scientist, 15 August 2008.
- Global Temperature Slowdown -- Not an End to Climate Change. UK Met Office, Dec 2009.
- Natural Climate Variability led to an Especially Cold 2008 [in North America]. American Geophysical Union, Editor's Choice, 8 December 2009. Summarizes A strong bout of natural cooling in 2008, Geophysical Research Letters s. Lett., 8 December 2009. According to the abstract, North American cooling in 2008 was driven by natural variability, temporarily overwhelming the warming from rising greenhouse gas concentrations. "The implication is that the pace of North American warming is likely to resume in coming years, and that climate is unlikely embarking upon a prolonged cooling," the article concludes.