CLIMATE CHANGE "FINGERPRINTS" NOW VISIBLE IN GLOBAL WEATHER EVERY DAY

Talk about thinking outside the box--

For decades now, climate scientists have worked to detect and measure the signal of human-caused climate change over time. They've revealed and warned us about changes in important variables such as atmospheric CO2, sea level and global average temperature; profound changes, but ones that take place over decades.

Climate change deniers, up to and including President Trump, have jumped on the fact that these incremental changes are swamped by much larger local daily and seasonal variability, making it difficult to link climate change to the weather people actually experience--with the fairly recent exception of super-storms or other extreme weather events that would have been extremely unlikely in the absence of global warming.

Now, a team of Swiss and Norweigian researchers has broken the mold. What would they see, they wondered, if they looked at variables such as temperature and humidity across space--the whole Earth--rather than over time. They were prompted to pursue this question by one of Trump's tweets using a major cold spell that hit much of the US to try to ridicule global warming.

"This lead to a lively debate about whether a single day could be informative at all about climate change," says climate scientist Reto Knutti, part of the Swiss-Norwegian research team. "Weather is not climate, yet we are seeing the imprint of climate change now in some single events, e.g. in the frequency of strong heatwaves. But what about the weather on an average day? Could we detect climate change in a single year, a month, a day?"

The answer they found is astonishing. Just by analyzing weather patterns across the globe they were able to detect the fingerprints of climate change on every day's weather since 2012.

Climate scientists can now detect signals of global warming in any day's weather

Image credit: NASA/MODIS

"Global weather is now in uncharted territory," says Knutti. "While locally of course we need a few decades for a signal to emerge from variability, the global information allows us to now detect climate change for any single day since early 2012."

The team used artificial intelligence (AI) to extract indicative patterns from the enormous mass of daily weather data around the globe. They could then test for the probability that the pattern for any given day could have appeared in the absence of climate change.

The daily weather patterns that most powerfully reveal the impact of climate change involve the global distribution of air temperature and humidity. Both variables were more pronounced over oceans than over land masses, and in the tropics compared to higher latitudes.

In retrospect, it may not be surprising that the cumulative heating effect of many decades of climate change is visible in the day-to-day distribution of temperatures across the globe. However, the researchers also found that they could still detect a strong climate change fingerprint in any given day's weather even without looking at temperature--simply from the pattern of atmospheric moisture around the world. "If we include humidity," says Knutti, "we can even detect climate change when we remove the global mean [temperature] signal for every single day, i.e. just by looking at the patterns."

If there was still any legitimate doubt that we humans have changed and are continuing to change the climate and the weather, this new way of charting the relationship between climate and weather should erase it.

Knutti writes, "In the last full IPCC report in 2013 we have shown that humans are the dominant cause of the long-term warming." We now demonstrate that since then we haven't had a single day of 'normal' weather globally. Yesterday was climate change, today is climate change, and tomorrow will be as well. We think this is a powerful message."

We couldn't agree more. The question is, is it powerful enough to get through to the deliberately deaf ears of our leaders?

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You can access the Nature Climate Change article describing this research here.

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REA

SOMETHING NEW TO WORRY ABOUT--QUASI-RESONANT AMPLIFICATION

Picture a river flowing down from the mountains to the plains. In the high country, where the river's descent is steep and hedged in by canyon walls, it's likely to follow a relatively straight path, basically tracing the shortest route down. Once it gets to the plains, however, there's no big difference between one path and another, and the river will begin to meander.

 Meandering river

Credit: Alana Whitman

Something similar is true for the jet streams, vast rivers of air that circle the globe from west to east, sometimes reaching speeds of 250 miles per hour. Like rivers, jet streams typically meander north and south. The size of those meanders and the speed with which they gradually drift eastward have major impacts on the weather. The UK, for example, was deluged by record floods in 2007 and again in 2012 when the jet stream looped far to the south and then stalled, unleashing extended periods of heavy rains.

Meandering polar jet stream

Credit: NASA/Goddard Space Flight Center 

That, in turn, gets us to climate change and quasi-resonant amplification (QRA). 

One of the most dramatic impacts of global warming and climate change is that the far north and south are warming much faster than the mid-latitudes and the tropics, a phenomenon known as polar amplification. What this means is that the temperature difference between the poles and the tropics-- which is what creates and drives the jet streams--is reduced. And like a river crossing a plain, this reduced gradient lets the jet stream meander farther north and south, and also tends to make the individual loops, known as Rossby waves, drift more slowly from west to east.

At the extreme, the meanders in the jet stream can form a stable sequence of exaggerated loops around the planet that can stay in place for weeks or months. This is known as quasi-resonant amplification  (QRA) and its results can be devastating. Warm, sunny days can extend into deadly heat waves, droughts and wildfires; while cool, rainy weather can linger, drenching an unlucky region with unprecedented rains and floods.

Michael Mann, a distinguished professor of atmospheric science and Pennsylvania State University, says that as of 2018 this phenomenon has now passed from the theoretical to the all-too-real and threatening. "It played out in real time on our television screens and newspaper headlines in the form of an unprecedented hemisphere-wide pattern of extreme floods, droughts, heatwaves and wildfires," he says.

Unfortunately, Mann adds, climate models indicate that such QRA-caused weather extremes will grow more frequent and more severe unless we get a handle on global warming. Recent research reinforces the link between reduced Arctic sea ice and the meandering jet stream, along with equally dire predictions. We can hope that humanity (and the politicians and corporations who hold the reins) will get their act together. In the meantime, however, we can all expect more QRAs and the devastating weather extremes they bring coming to a region near us.

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You can read an earlier post on this subject here.

For more detail on arctic warming and its impacts on our weather click here.

And for a new study that shows that these destructive "blocking events" will cover greater areas as the world heats up, navigate to this URL.

(As-yet unpublished research shows that these stalled atmospheric waves have the potential to cut crop production across much of the northern hemisphere.)

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SIGNS OF THE TIMES: PROFESSORS OF CYBERPSYCHOLOGY AND EXTREME-WEATHER RISKS

My email today included notices of two new academic posts that I found eye-opening:

KIT, the Karlsruhe Institute of Technology, in Germany, has endowed a new professorship dedicated to the study of the risks from extreme weather events. I guess they haven't been convinced by the arguments of climate-change deniers.

Tornado, Andarko Oklahoma, May 1999/Credit Dizpics1/Wikipedia
Intense, large-scale tornado outbursts like this are happening more frequently

The University of Warwick, in the UK, has appointed its first cyberpsychologist, Monica Whitty. Professor Whitty joins other researchers at the university's Cyber Security Centre. Her focus is "on the human element . . . behaviour online to identify cyber criminals and in turn protect people from becoming victims."

Maybe if Hillary Clinton had known about Dr. Whitty a year or two ago, we'd have a different person taking the oath of office on January 20.