December 22, 2012 — andyextance

This has been another year of striking climate events and records – but they seem to be happening so much more often today that their effect on me has weakened. That’s pretty cold-hearted, I admit. ‘Extreme weather’ is having terrible effects on peoples’ lives all around the world. But the truth is that we can only handle so many problems before becoming too numbed and overwhelmed to act. And last year, Stefan Rahmstorf and coworkers at the Potsdam Institute for Climate Impact Research showed temperature records are much more likely today than in a stable climate. “I don’t think many people appreciate how much the odds for such extremes have increased due to global warming,” he told me at the time. “I certainly didn’t until we had performed this study.” So it’s hardly surprising if we begin to get complacent when records are flowing thick and fast. But when I actually faced up to what’s happened in the climate this year, it was intriguing how well you could see global warming’s fingerprint.

Warming’s most dramatic effects have long been obvious in the Arctic, and 2012 was no different. Images from three satellites showed that almost Greenland’s entire ice sheet surface was temporarily melted by July 12. That’s the largest area in over 30 years of satellite observations. Then, on September 16, sea ice in the Arctic reached a record annual minimum area of 1.32 million square miles, approximately half the size of the average annual minimum for 1979 to 2000. Just two weeks later, Antarctic sea ice covered its highest area on record at the peak of winter, at 7.49 million square miles. In case you think that’s a natural balance that shows the planet isn’t warming, it’s worth noticing the scale of the changes. The Antarctic record is 193,000 square miles higher than its average maximum area for the last 30 years. That’s much less than the 1.32 million square miles the Arctic lost compared to its long-term average.

Jet streams and UK floods

The Arctic melt impacts climate in the rest of the world Jiping Liu, now at University at Albany, State University of New York, told me in March. “Stronger westerly winds, also known as the jet stream, keep cold Arctic air confined in the polar regions,” he said. “But reduced Arctic sea ice can result in a weaker and much more variable jet stream. When the jet stream is weak we instead have atmospheric blocking circulations. These let cold, Arctic air mass into lower latitudes bringing cold conditions which favour snowfall.” That could be an important consideration in the UK, where I live. April 2012 was the wettest in the country’s records, which date back to 1910. That was partly down to the jet stream flowing over the UK, rather than to its north as it has done in the past. The UK’s Met Office also noted a potential link between the unusual jet stream and the Arctic melt.

The UK’s April wetness record came just as researchers showed that climate change is strengthening the cycle of rain falling and evaporating by twice as much as models predict. I asked one of the team, Susan Wijffels from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Hobart, Australia, how the finding was linked to the wet UK. “It’s associated with the fact that a warmer atmosphere can shuttle and carry around more water and energy,” she said. “Flood periods will be more intense and drought periods will be hotter, drier, leading to more water deprivation during those periods.” The country then went on from a wet spring to see its wettest summer for 100 years, and its second wettest on record. The UK then saw widespread flooding in November – including in my hometown, Exeter. Looking back as I write this in December, Wijffels’ comments look all the wiser.

More intense, less frequent

People in the US might think the same, as the country saw the most severe and extensive drought in 25 years. And the country should brace for more of the same as climate change continues, Christopher Schwalm, from Northern Arizona University in Flagstaff told me in August. He has found that conditions the US Midwest saw in its 2000-2004 drought will become normal by the end of the 21st century. He backs Wijffels’ point about the changes in the water cycle, that droughts are the flipside to flood periods. “Precipitation will happen in spurts, more intensive rainfall in a relatively short period of time,” he said. “Similarly, the amount of time between such events is expected to increase. So we will see fewer but more intense rainfall events, and therefore more droughts.”

Climate scientists have also projected that storms will change in a similar pattern, becoming more intense but fewer. But overall, that will add up to a “greatly increased” number of people threatened by tropical cyclones and the disasters they can cause over the next 20 years. So said research published in February by Bruno Chatenoux from the Global Change and Vulnerability Unit at the United Nations Environment Program in Geneva, Switzerland. That again seems especially relevant with 2012 being a year for notable storms. In October Hurricane Sandy hit the Caribbean and US, causing a record storm surge in New York City. Storm intensification in the Atlantic is down to both increasing greenhouse gas and reducing soot emissions, Gabriel Vecchi at the US National Oceanographic and Atmospheric Administration (NOAA) in Princeton, New Jersey told me earlier this month. Then, in December Typhoon Pablo swept away towns in the Phillippines, killing hundreds. It also became the most southerly typhoon on record, the second in a year to reach the Philippine island of Mindanao.

It’s not currently possible to definitely say whether any given weather event is caused by climate change – although climate scientists are trying to establish links. But 2012 saw a series of incidents that fit with climate scientists’ projections and harmed people, their homes and livelihoods. Sometimes it’s hard to absorb their implications – but they’re worth thinking about if you get the chance.

Journal References:

Newell, B., & Pitman, A. (2010). The Psychology of Global Warming Bulletin of the American Meteorological Society, 91 (8), 1003-1014 DOI: 10.1175/2010BAMS2957.1

Rahmstorf, S., & Coumou, D. (2011). Increase of extreme events in a warming world Proceedings of the National Academy of Sciences, 108 (44), 17905-17909 DOI: 10.1073/pnas.1101766108

Liu, J., Curry, J., Wang, H., Song, M., & Horton, R. (2012). Impact of declining Arctic sea ice on winter snowfall Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1114910109

Durack, P., Wijffels, S., & Matear, R. (2012). Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000 Science, 336 (6080), 455-458 DOI: 10.1126/science.1212222

Schwalm, C., Williams, C., Schaefer, K., Baldocchi, D., Black, T., Goldstein, A., Law, B., Oechel, W., Paw U, K., & Scott, R. (2012). Reduction in carbon uptake during turn of the century drought in western North America Nature Geoscience, 5 (8), 551-556 DOI: 10.1038/ngeo1529

Villarini, G., & Vecchi, G. (2012). Multi-Season Lead Forecast of the North Atlantic Power Dissipation Index (PDI) and Accumulated Cyclone Energy (ACE) Journal of Climate DOI: 10.1175/JCLI-D-12-00448.1

Peduzzi, P., Chatenoux, B., Dao, H., De Bono, A., Herold, C., Kossin, J., Mouton, F., & Nordbeck, O. (2012). Global trends in tropical cyclone risk Nature Climate Change, 2 (4), 289-294 DOI: 10.1038/nclimate1410

Pall, P., Aina, T., Stone, D., Stott, P., Nozawa, T., Hilberts, A., Lohmann, D., & Allen, M. (2011). Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000 Nature, 470 (7334), 382-385 DOI: 10.1038/nature09762

Min, S., Zhang, X., Zwiers, F., & Hegerl, G. (2011). Human contribution to more-intense precipitation extremes Nature, 470 (7334), 378-381 DOI: 10.1038/nature09763