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.

Quoth NASA:

Record warmth in 2005 is notable, because global temperature has not received any boost from a tropical El Niño this year. The prior record year, 1998, on the contrary, was lifted 0.2°C above the trend line by the strongest El Niño of the past century.

Global warming is now 0.6°C in the past three decades and 0.8°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 0.2°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.


  1. Peter Curtis - July 17, 2009 at 8:49 pm -

    Good scientists are skeptics, that is there is it always better to doubt than not. To not doubt heads toward a religious attitude. The most disturbing thing about the whole misnamed climate change debate is that it is so dogmatic. Anyone who raises a question or a doubt is dismissed as a denier. This is something akin to original sin. The last big scare was planet cooling and then over population, now it is overheating. Science does not proceed by consensus, that would be disastrous becuase that would mean we cease to question and doubt. Consensus is a social political tool that is useful for making decisions about human actions but alas nature has no interest in our social actions. BTW nothing is conclusive. I have heard that being a denier is akin to be a flat earther. We should remind ourselves that even when the theologins were proposing such therioies there were a small minority of skeptics challenging them on that one too.

  2. admin - July 17, 2009 at 10:14 pm -

    Hi Peter,

    Science is also about peer review. To my knowledge, there are no climate change deniers who have been willing to subject their views to peer review.

    This particular scientific debate started in the 1890s, and was roundly shouted down by climate change deniers up until the last decade or so when the evidence became overwhelming.

    A fast response to climate change (anthropogenic or not) is simply good risk management.

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