Fifteen Years of Cooling
July 15, 2009
Surely I’ve already put a link to this famous graph, which answers the proposition put by climate change denialists that there has been a decade (or fifteen years of cooling).
Australia’s most famous climate denialist is Senator Steve Fielding, an accidental senator who’s been briefed by several denialist-scientists that anthropogenic climate change is a fraud. He’s been carrying around a graph that seems to show that the globe has been cooling.
There is little doubt that there is a scientific consensus that greenhouse gases are causing climate change.
Fielding’s graph to the right, which starts in 1995, is a classic example of cherry picking.
The five hottest years on record have occurred since 1998, with the hottest ever being 2005. However, if you take simply the last decade or fifteen years, then the trend line is down. This is simply misleading. Yearly variations in temperature over a short period of time is weather, not climate. Climate occurs over decades or centuries.
A longer picture of the climate shows that there has been rising since the 1880s. This NASA chart (the article is linked above) gives a longer view. This shows that there has been a clear increase in global mean surface temperatures.
Record warmth in 2005 is notable, because global temperature has not received any boost from a tropical El NiÃ±o this year. The prior record year, 1998, on the contrary, was lifted 0.2Â°C above the trend line by the strongest El NiÃ±o of the past century.
Global warming is now 0.6Â°C in the past three decades and 0.8Â°C in the past century. It is no longer correct to say that “most global warming occurred before 1940”. More specifically, there was slow global warming, with large fluctuations, over the century up to 1975 and subsequent rapid warming of almost 0.2Â°C per decade.
Recent warming coincides with rapid growth of human-made greenhouse gases. Climate models show that the rate of warming is consistent with expectations (5). The observed rapid warming thus gives urgency to discussions about how to slow greenhouse gas emissions (6).
The map shows that current warmth is nearly ubiquitous and largest at high latitudes in the Northern Hemisphere. Our ranking of 2005 as warmer than 1998 is a result mainly of the large positive Arctic anomaly. Excluding the region north of 75N, 1998 is warmer than 2005. If the entire Arctic Ocean were excluded, the ranking of 2005 may be even lower.
Now, I’d say this is conclusive.