Did global warming really stop in 1998?

Global Temperature Land-Ocean Index (source: NASA Goddard)

Anthropogenic climate change deniers insist that any positive trend there may have been in the Earth’s global average surface temperature levelled off in 1998. Now this myth has repeatedly been demolished by people who know what they are talking about, but still it persists within the closed, ideological ecosystem of climate denialism.

Setting aside the abnormally strong El Niño event of 1998 which led to record high temperatures and turned the temperature trend negative when measured from that point, is there other evidence of a slow-down or halt in global warming? Not according to Jim Hansen and others at the NASA Goddard Institute for Space Studies in New York, who have released for discussion a draft of a new paper on global surface temperature analysis. Note that this work has yet to be peer-reviewed; for now the paper is available for discussion, and the authors have pointed out areas that must be improved before submission to a learned journal.

Hansen et al.’s draft paper is long, and includes a number of points of interest. One is that, contrary to popular belief, global warming did not stop in 1998, and the rate of warming has not fallen in the past decade. Figure 21 of Hansen’s paper shows this clearly. It may take a five year running mean of the data to reveal the persistent positive trend in surface temperature, but such averaging is required to minimise the effect of El Niño variability. The authors’ conclusion from the data that there has been no reduction in the global warming trend which began in the late 1970s seems entirely justified.

Another point worth noting is that this year’s abnormally cold northern hemisphere winter coincides with the most extreme negative phase of the Arctic Oscillation since 1950. While we cannot rule out a repeat performance, Hansen and his coworkers point out that there is a trend in the Arctic Oscillation toward more positive values, and stress that the anthropogenic global warming trend has a larger effect than the Arctic Oscillation on regional as well as global temperatures. The freezing winter from which we have just emerged is freak weather, not climate.

In an email announcing the draft paper, Hansen writes…

“Somehow we have to do a better job of communicating. The tricks being used by people supporting denial and business-as-usual are recognizably dirty, yet effective. We are continually burdened by sweeping FOIA (Freedom of Information Act) requests, which reduce our ability to do science and write it up (perhaps this is their main objective), a waste of tax-payer money. Our analyses are freely available on the GISS web site as is the computer program used to carry out the analysis and the data sets that go into the program.”

“It seems that a primary objective of the FOIA requestors and the “harvesters” is discussions that they can snip and quote out of context. On the long run, these distortions of the truth will not work and the public will realize that they have been bamboozled.”

“[H]arvesters” refers to automated software used by climate deniers to collect text and graphics from public and private sections of the Goddard Institute web server, following which the data are published elsewhere in cherry-picked form. Given that the climate deniers’ amorality knows no bounds, let us hope that Hansen’s final sentence above is not just wishful thinking.

Further reading: Hansen et al., “Current GISS Global Surface Temperature Analysis”, NASA Goddard Institute for Space Studies, (discussion draft, 2010)