"Fingerprint" of the climatic impact of humanity seen in the seasons

that humans are responsible for modern warming, it is that they have more than just meteorological data with which to work. There are many places where a human cause can be identified if you know how to dust off your fingerprints. For example, while the lower atmosphere is warming up, the stratosphere is cooling down. That's what you expect when greenhouse gases – rather than the Sun – are behind the warming.

A new study by Ben Santer of the Lawrence Livermore National Laboratory has looked for fingerprints in a new place: the seasonal cycle of temperatures. The ideal tool to analyze this is the recording of the global temperature produced by the satellites, which began monitoring them in 1979. This means that they do not go back as far as the weather station records , but the data set is now long enough to be useful

Hot and Cold

While everyone uses the same satellites, several different groups actually maintain separate sets of data on the temperature of the satellites. satellites. This is because the measurements are far from simple, and a ton of work goes into all the treatments needed to spit the temperature charts. As a result, the different datasets do not always match each other perfectly well, nor with those analyzed with previous versions of their processing algorithm. Thus, in this study, the researchers used the two most recent versions of three different data sets

Each set of data follows a few different layers of the atmosphere. A record covers the lower troposphere, the first 10 kilometers above the surface of the Earth. Although this is the closest to the surface temperatures in which we live, it is also the most difficult measure to obtain. A cleaner record focuses on the average troposphere, a little higher

By following the difference between the coldest winter months and the hottest summer months – the amplitude of the annual cycle of the seasons – some interesting regional models appear. (You can see this in the image at the top of the page.)

If you average the mid-latitude band of the northern hemisphere, there is a larger seasonal temperature change only in the southern hemisphere, because there is a greater area of ​​land (which heats up and cools to higher extremes than the ocean). But this seasonal cycle has also increased measurably since 1979 – even more so in the Northern Hemisphere – due to summer temperatures in the atmosphere that are increasing faster than winter temperatures.

In the tropics, the seasonal cycle is fundamentally unchanged. In contrast, near the poles, the satellites show that the oscillation of seasonal temperature has decreased

There is one interesting exception that does not show this model: the University's data set. Alabama in Huntsville, led by Roy Spencer. and John Christy (two of the few voiceless scientists who reject or downplay climate change of human origin). This dataset looks totally different in Antarctica. In fact, the strangeness in the Huntsville data only appears in its last update and seems to reflect a problem of managing the transition between first and second generation satellites. There is a history of managers of other large sets of satellite data discovering errors in the Huntsville algorithm, and this seems to add another example

Models and Reality

So what do these modified seasonal patterns mean? ? To answer this question, Santer and the other researchers used a series of simulations of major climate models. This includes long simulations of an immutable climate (before the industrial revolution), as well as simulations of the warming caused by humans until 2016. This allowed them to analyze the models. seasonal patterns that climate models predict for a warmer world, as well as

Researchers have found that models predict this seasonal trend almost exactly: larger seasonal fluctuations in mid-latitudes (especially for the northern hemisphere) , few changes in the tropics and smaller fluctuations in the tropics. l & # 39; Antarctica. The models also correctly predict a smaller seasonal cycle around India and Southeast Asia, which departs from the general trend of mid-latitudes.

The only disparity is in the Arctic. predicted average model. About a third of the models show a decline, but not the rest. The models have generally underestimated the loss of Arctic sea ice, and this is perhaps the key here, since sea ice loss is an important factor in seasonal cycle change.

It is we, version 857

the changes observed by satellite indicate a warming caused by man, the researchers used a signal-to-noise analysis. Using pre-industrial-scale simulations to estimate the extent of natural variability, the analysis showed that seasonal patterns observed in the middle troposphere clearly emerged above noise. This makes it a clear manifestation of the models predicted by the models. It's even clearer than the change in global average temperatures, in fact, because seasonal trends across entire latitude bands will not vary much in a stable climate.

While they were there, the researchers repeated these analyzes for a more direct measure of climate change: the average annual temperature, analyzed at different locations around the world. They write: "We note here that, for the annual average [mid-troposphere temperatures] the estimated ratios [signal-to-noise] exceed 4.4 for temperature changes over 38 years of the satellite record. Overall, they conclude, "The best explanation for these results is that basic physics and basic physical mechanisms are leading to natural variability."

Large scale changes in [seasonal patterns]. For tropospheric temperature, an anthropogenic signal is now evident in the seasonal cycle itself. "

This is just one more reason for scientists to be sure that humans are driving climate change."

Science 2018 DOI: 10.1126 / science.aas8806 (About DOI).