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Global Warming Since 1997 Underestimated By Half
Layzej writes "A new paper shows that global temperature rise of the past 15 years has been greatly underestimated. The reason is that the weather station network covers only about 85% of the planet. Satellite data shows that the parts of the Earth that are not covered by the surface station network, especially the Arctic, have warmed exceptionally fast over the last 15 years. Most temperature reconstructions simply omit any region not covered. A temperature reconstruction developed by NASA somewhat addresses the gaps by filling in missing data using temperatures from the nearest available observations. Now Kevin Cowtan (University of York) and Robert Way (University of Ottawa) have developed a new method to fill the data gaps using satellite data. The researchers describe their methods and findings in this YouTube video. 'The most important part of our work was testing the skill of each of these approaches in reconstructing unobserved temperatures. To do this we took the observed data and further reduced the coverage by setting aside some of the observations. We then reconstructed the global temperatures using each method in turn. Finally, we compared the reconstructed temperatures to the observed temperatures where they are available... While infilling works well over the oceans, the hybrid model works particularly well at restoring temperatures in the vicinity of the unobserved regions.' The authors note that '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 first link in the summary links to the paper published by the Journal of the Royal Meteorological Society.. The youtube video makes the science accessible to the layman.
Fail.
Cowtan and Way circumvent both problems by using an established geostatistical interpolation method called kriging – but they do not apply it to the temperature data itself (which would be similar to what GISS does), but to the difference between satellite and ground data. So they produce a hybrid temperature field. This consists of the surface data where they exist. But in the data gaps, it consists of satellite data that have been converted to near-surface temperatures, where the difference between the two is determined by a kriging interpolation from the edges. As this is redone for each new month, a possible drift of the satellite data is no longer an issue.
Prerequisite for success is, of course, that this difference is sufficiently smooth, i.e. has no strong small-scale structure. This can be tested on artificially generated data gaps, in places where one knows the actual surface temperature values but holds them back in the calculation. Cowtan and Way perform extensive validation tests, which demonstrate that their hybrid method provides significantly better results than a normal interpolation on the surface data as done by GISS.
The only thing in TFS is that they cover 85% of the globe, where does the "half" come from?
From the paper, which actually found 2.5 times as much warming by leveraging satellite data as the CRUtemp does by ignoring the unobserved region. The paper shows that the Arctic is warming at about eight times the pace of the rest of the planet. This is not an unexpected finding: see polar amplification
Why do you think the IPCC no longer uses the Hockey-stick graph?
They don't use Mann's original hockey stick graph from 1998 any more because it's 15 years old and numerous other newer reconstructions have been done since then. But if you take a look at Chapter 5 - "Information from Paleoclimate Archives" of the IPCC AR5 - WG I report you'll find that figures 5.7 & 5.8 still look remarkably like the original hockey stick graph. So they've got newer versions of it.