A recent article was published in Nature claiming the observed warming since the mid-1800s is underestimated because of missing data from geographically remote regions of earth in the earlier part of the period of record.
Presumably they mean the polar regions of the globe. As such, this means observed global temperatures of the earlier time are biased toward a warmer globe, or global temperatures were really cooler than previously thought. They conclude the actual trend of global warming since the mid-1800’s is underestimated by about 24%.
The authors performed an apples-to-apples comparison in terms of spatial data coverage and using a climate model. They found not only the missed warming but that the climate models actually do represent the climate changes of the last sesquicentennial very well.
While the effort to make a better comparison is laudable, such a comparison is not likely to improve meaningfully upon our estimates of climate change from the mid-1800s.
First, it is impossible to make such a comparison with today’s observations. In the mid-1800s, only Europe, the Eastern USA, and well-travelled shipping routes were regions with dense and continual data coverage. Of course the polar regions of the globe were not well-sampled at the time, representing about 14 percent of the global surface area.
This is a significant portion of the globe. However, the analysis cannot take into account that instrumentation, the quality of the instrumentation, measurement practice, and station locations have changed since then, in some cases substantially. This will impact the uncertainty of the data quality, which was presumably larger then than now.
Second, there is another significant flaw in their conclusions. Their result assumes that all the uncertainty in the data must result in an underestimation of warming, or the error in the previous records lead to a unidirectional find, either of which is unlikely.
This means it would be possible to present scenarios which also claim that the warming is overestimated as well, depending on how the data from the earlier times is augmented and the accounting of uncertainty.
Additionally, given the range of uncertainties in today’s model output, as well as differences found between the variables such as temperature in primary re-analysis data sets, it is difficult to draw meaningful comparisons of recent global temperatures with those of the past.
Third, we could take a look at variability in global climate, as climate variability is one of the more important factors influencing near-term projections in economic and agricultural activity. Others commenting on this study remind us that climate variability in the polar regions of our planet is observed to be greater than that in the mid-latitudes or tropics. Thus, if the current temperature records are biased toward a smaller warming, then surely they are biased toward less variability. This means it is likely that the relative warmth of the late 1920s to mid-1940s is closer to that of the current period than previously thought.
While is it universally agreed upon that earth’s climate has warmed since the mid-1800s, quantifying the precise amount is nearly impossible. Nonetheless, the most often quoted value is around 1.0o C.
But as stated by the article’s authors, we are missing just over 0.2o C of the warming. This missing warming is not insignificant from a policy making standpoint given that the Paris Agreements of last year agreed to keep the amount of warming since the industrial revolution below 1.5o C. It is virtually certain that the results of papers like this will be used as justification for even more urgent action on global warming.
If the conclusions of the authors’ paper are correct and the warming of the last 150 years was underestimated, then the climate system is a little more robust than previously thought.
This is a point against lowering the post-industrial ‘warming barrier’ from 2.0o C to 1.5o C. Also, the same climate models used in the authors’ study show an additional warming of 1.0o to 3.3o C by the end of this century. This will continue the calls for urgency in action on climate change.
But, regardless of which global temperature trend of the last 150 years is the correct one, it cannot be argued that agriculture and technology have not advanced by leaps and bounds. They have, in concert with, and maybe partly because of, warming, and more people on earth are now living better lives than in 1850.
But given the uncertainty in past and future climate change and the fact that people are living better now, why is there so much urgency to make and strengthen agreements, such as Paris, to combat climate change as an excuse to convert to command economies?