Human influence detected in changing seasons

Human influence detected in changing seasons
Trends in the amplitude of the annual cycle of tropospheric temperature. Trends are calculated over 1979 to 2016 and are averages from a large multi-model ensemble of historical simulations. The most prominent features are pronounced mid-latitude increases in annual cycle amplitude (shown in the red colors) in both hemispheres. Similar mid-latitude increases occur in satellite temperature data. Trends are superimposed on NASA’s “blue marble” image. Credit: Lawrence Livermore National Laboratory

For the first time, scientists from Lawrence Livermore National Laboratory (LLNL) and five other organizations have shown that human influences significantly impact the size of the seasonal cycle of temperature in the lowest layer of the atmosphere.

To demonstrate this, they applied a so-called "fingerprint" technique. Fingerprinting seeks to separate human and natural influences on . It relies on patterns of climate change—typically patterns that are averaged over years or decades. But in the new research appearing in the July 20 edition of the journal Science, the team studied seasonal behavior, and found that human-caused warming has significantly affected the seasonal temperature cycle.

The researchers focused on the troposphere, which extends from the surface to roughly 16 kilometers in the atmosphere at the tropics and 13 kilometers at the poles. They considered changes over time in the size of the of at different locations on the Earth's surface. This pattern provides information on temperature contrasts between the warmest and coldest months of the year.

Away from the moderating effects of oceans, mid-latitude regions of Northern Hemisphere continents have a large seasonal cycle of atmospheric temperature, with frigid winters and hot summers. Satellite temperature data are consistent with models that project that this seasonal "heartbeat" is becoming stronger with human emissions of carbon dioxide.

Other features common to the observations and model simulations are small changes in the tropical seasonal temperature cycle, and a decrease in the size of the seasonal cycle in the Antarctic region.

"Our results suggest that attribution studies with the changing seasonal cycle provide powerful and novel evidence for a significant human effect on Earth's climate," said LLNL climate scientist and lead author Benjamin Santer.

Earth's climate is simultaneously affected by different external and internal factors. Examples of external influences are natural changes in the sun's energy output and human-caused increases in atmospheric concentrations of greenhouse gases. Internal influences include a wide range of natural cycles, such as the El Niño/Southern Oscillation and the Interdecadal Pacific Oscillation. Variations in these and many other internal and external factors have driven changes in historical climate.

Since the inception of climate fingerprint research in the late 1970s, scientists have used pattern recognition methods to detect unusually large changes in climate and to attribute these changes to different external influences. Initial studies concentrated on surface and . Later fingerprint research considered changes in a wide range of variables, including ocean heat content, the hydrological cycle, atmospheric circulation, sea ice extent and the behavior of extreme events.

In the new research, the team examined model simulations driven by historical changes in human factors. A prominent feature of these simulations is that at mid-latitudes, the size of the seasonal temperature cycle increases markedly. This increase results from larger warming in each hemisphere's summer season. In turn, larger mid-latitude summer warming appears to be partly due to summer drying of the land surface.

Because of differences in the heat capacity of land and ocean, and because there is substantially more land in the Northern Hemisphere, mid-latitude increases in the seasonal temperature cycle are larger in the Northern than in the Southern Hemisphere. Similar large-scale patterns of seasonal cycle change occur in satellite tropospheric temperature data. The "pattern match" between the human influence fingerprint and the satellite patterns of seasonal cycle change was highly significant. The match was unlikely to be due to natural internal climate variability.

The satellite tropospheric temperature data used in the Science paper show global-mean annual average warming of roughly 1.25 degrees Farenheit from 1979 to 2016. The causes of this annual average warming signal have been the subject of many previous studies. But until the new research was conducted, no formal fingerprint study had been performed with the changing seasonal cycle of tropospheric .


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A human-caused climate change signal emerges from the noise

More information: Benjamin D. Santer et al. Human influence on the seasonal cycle of tropospheric temperature, Science (2018). DOI: 10.1126/science.aas8806
Journal information: Science

Citation: Human influence detected in changing seasons (2018, July 20) retrieved 20 August 2019 from https://phys.org/news/2018-07-human-seasons.html
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Jul 20, 2018
One more example of Santer trying to pass off one of his arcane computer models as empirical observation.

Jul 20, 2018
I think he's actually trying pass off the empirical observations as empirical observations. The physical model results just significantly match the empirical observations, which is nice, and gives insights into the empirical observations. Given that it's been shown that even simple physical models do a good job at matching the observations, it's been a while since I've heard the anti-science movement claim models have problems. But oftentimes this information takes a while to trickle down to the lower echelons of political movements.

Jul 20, 2018
Yep. It seems like all of the climate change deniers lost interest as soon as their Russian funding ran out.

Jul 21, 2018
even simple physical models do a good job at matching the observations

No they don't. They never have. The Technical Summary of IPCC AR5 illustrated how bad the models are at predicting global temperature:

https://www.ipcc....S-14.jpg

The models track measured temperatures nicely from 1980 to 2000, which they should since they were calibrated to do that. But after 2000 they predict much more warming than measured and they continue to diverge more from measurements each subsequent year.

Using CMIP5 models to identify a human signature in temperatures is ridiculous given their demonstrable inaccuracy. Then mapping that false human signature onto measurement data and claiming that it shows a human influence is scientific prestidigitation. Or scientific malpractice.

Jul 21, 2018
What will it take for aksdad to stop posting links that directly contradict his point?

Jul 23, 2018
What will it take for aksdad to stop posting links that directly contradict his point?


This is an easy one! He should actually read what he links to!!

Unfortunately, he is too caught up in his own personal belief to actually read about the subject. He already knows, you see. There is nothing left he can learn.

Jul 23, 2018

What will it take for aksdad to stop posting links that directly contradict his point?


This is an easy one! He should actually read what he links to!!

Unfortunately, he is too caught up in his own personal belief to actually read about the subject. He already knows, you see. There is nothing left he can learn.


I ponder a world were aksdad is not a professional troll but is, in fact, a normal person who just can't read a graph. Poor, sad, innumerate aksdad.

Jul 29, 2018
Unbelievable that this science site is promoting global warming. More unbelievable is that so many people bought this scam, simply unbelievable. Poor little CO2...do you people understand that CO2 is colorless, odorless and not toxic? It is heavy, 1.5 specific gravity. Air is 1.0. THINK about that. Like Propane gas CO2 seeks the lowest spot possible pushing the air out of a 'hole' and no air no animals can live. There is only 400 ppm CO2 in the atmosphere and I still don't know how they test THAT aspect because CO2 is a 'poorly mixing' gas...before mankind, atmospheric CO2 was an awful lot higher 2000 ppm. Happy plants, happy oceans no 'greenhouse' heating. If we get down to 150ppm plants will die then we all die. Do you guys know about the Grand Solar Minimum we are now in? Happens every couple hundred years like clockwork. Look up the Maunder, Centennial, Dalton and the current one is Eddy. We are well into a Global Cooling. Why we weren't getting ready for this is amazing.

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