Computer simulations predicted years ago that, on average, warming would increase the closer you get to the poles.
University of Ottawa
http://www.uottawa.ca/media/media-release-2883.html
OTTAWA, November 14, 2013 — An interdisciplinary team of researchers have found the “missing heat” in the Earth’s climate system, casting doubts on suggestions that global warming has slowed or stopped over the past decade.
Observational data, on which climate records are based, covers only 84% of the planet and largely excludes the polar regions and parts of Africa.
Now, University of York computational scientist Kevin Cowtan and University of Ottawa cryosphere specialist and PhD candidate Robert Way have reconstructed the “missing” global temperatures by combining satellite data with surface observations gathered from weather stations and ships on the peripheries of the unsampled regions.
The new research published in the Quarterly Journal of the Royal Meteorological Society, shows that the Arctic is warming about eight times faster than the rest of the planet. Previous studies by the UK Met Office, which were based on the HadCRUT4 dataset only covers about five-sixths of the globe, suggest that global warming had slowed substantially since 1997. However, the new research suggests that given the addition of the “missing” data, the warming rate since 1997 has been two-and-a-half times greater than shown in the Met Office studies. Evidence for the rapid warming of the Arctic includes observations from high latitude weather stations, radiosonde and satellite observations of temperatures in the lower atmosphere, and reanalysis of historical data.
He said that “there’s a perception that global warming has stopped but, in fact, our data suggests otherwise. But the reality is that 16 years is too short a period [from which] to draw a reliable conclusion. We find only weak evidence of any change in the rate of global warming.”
Robert Way added that “changes in Arctic sea ice and glaciers over the past decade clearly support the results of our study. By producing a truly global temperature record, we aim to better understand the drivers of recent climate change.”
==========================================
From the University of York:
http://www-users.york.ac.uk/~kdc3/papers/coverage2013/background.html
-----
The temperature change for any individual year is not very large (and less than the Met Office uncertainty estimates), but together they make a significant difference to recent temperature trends. This highlights the danger of drawing conclusions from trends calculated over short periods.
Scientific context
Climate scientists have traditionally looked at climate over long periods - 30 years or more. However media and public interest in shorter term trends has focussed attention on the past 15-16 years. Short term trends are much more complex because they can be affected by many factors which cancel out over longer periods. To interpret the 16 year trend, it is necessary to take into account all of these factors, including volcanoes, the solar cycle, particulate emissions from the far East and changes in ocean circulation. The bias addressed by this paper is just one piece in that puzzle, although a largish one.
-----
Part of the impetus for our work came from a Met Office press release in 2009, which stated ‘… HadCRUT is sampling regions that have exhibited less change, on average, than the entire globe over this particular period … We therefore infer with high confidence that the HadCRUT record is at the lower end of likely warming.’.
-----
Did the Met Office get it wrong?
No. The Met Office have been reporting the existence of this bias since 2009, although the issue has not received widespread media coverage. The Met Office also provide uncertainty estimates for their temperature data: our results fall within the 95% confidence intervals of the annual data.
-----
Is the 16 year trend statistically significant?
This often asked question usually springs from a misunderstanding of statistics. Most people hearing the phrase ‘the trend is not significant’ interpret that as evidence that there is no trend. This is an error: drawing a conclusion from the failure of statistical significance test is called the ‘null hypothesis fallacy’. The implication in this case is that 16 years is too short a period to draw a conclusion.
==================================
http://www.realclimate.org/index.php/archives/2013/11/global-warming-since-1997-underestimated-by-half/#more-16173
------
While short term trends are generally treated with a suitable level of caution by specialists in the field, they feature significantly in the public discourse on climate change.
------
The public debate about the alleged “warming pause” was misguided from the outset, because far too much was read into a cherry-picked short-term trend. Now this debate has become completely baseless, because the trend of the last 15 or 16 years is nothing unusual – even despite the record El Niño year at the beginning of the period. It is still a quarter less than the warming trend since 1980, which is 0.16 °C per decade. But that’s not surprising when one starts with an extreme El Niño and ends with persistent La Niña conditions, and is also running through a particularly deep and prolonged solar minimum in the second half. As we often said, all this is within the usual variability around the long-term global warming trend and no cause for excited over-interpretation.
No comments:
Post a Comment