The 2008 climatological report: partly cloudy. Or partly sunny — it depends on your point of view, which underscores why it can be so easy to misunderstand the mechanism of climate change. The World Meteorological Organization (WMO) on Tuesday released its weather analysis for the year and found that 2008 has been the coolest year since the turn of the century. Using data gathered from Britain's Hadley Centre, the University of East Anglia and the U.S. National Oceanic and Atmospheric Association (NOAA), the WMO reported that the average global temperature in 2008 was 57.74 degrees F (14.3 degrees C), cooler than the past several years. That's due in part to the chilling action of the climatological effect known as La Niña, which cooled the Pacific.
So does that mean global warming has ceased?
Afraid not. Even though 2008 is cooler than the past several years, it's still likely to rank as the 10th warmest year since the beginning of climate records in the 1850s. And despite the cooling of the Pacific, several parts of the Earth — especially the Arctic, where sea ice melted to its second lowest level ever this summer — were far above normal temperatures. Globally, 2008 was about 0.56 degrees F (0.31 degrees C) warmer than the annual average between 1961 and 1990. But if the heat seemed to have been turned down during 2008, that could owe to the fact that the gradual warming trend has changed our idea of a normal temperature. As Myles Allen, head of the Climate Dynamics Group at Oxford University, explains, "Globally, this year would have been considered warm, even as recently as the 1970s or 1980s, but [it would have been] a scorcher for our Victorian ancestors."
During 2008, we kept pouring billions of tons of greenhouse gases into the atmosphere, so it's easy to assume that the climate would keep warming uniformly — and therefore to use evidence to the contrary as grounds for doubting that human activity really causes climate change. But the climate and the weather are not the same thing: we experience only the weather, which is the day-to-day, sometimes hour-to-hour changes of temperature, precipitation, wind and more. The climate, on the other hand, refers to the cumulative average of the weather around us over decades, centuries and longer.
So we can't track global warming through changes in the weather, even from one year to the next. Instead we need to look at the long-term trends, and here the evidence is undeniable. "The trend for warming is still there," says Michel Jarraud, the secretary general of the WMO. There will be oscillations, up and down trends, thanks to other climatological factors like La Niña, its warming opposite El Niño, even large volcanic eruptions, which can throw sulfur into the atmosphere and temporarily cool the planet. But unless we reverse the steady increase in greenhouse-gas emissions, over the long term, the world's temperature is going in one direction: up.