@NOAA: The atmosphere and Arctic sea ice: Who’s the dog, and who’s the tail?

From NOAA (Tom Di Liberto):

In recent years, a popular debate has been occurring within the climate community. No, it’s not whether climate change is occurring and caused by humans. (It is.) Instead, it’s regarding how much of an effect, if any, the rapid warming of Earth’s frozen cake-topper we call the Arctic, and the corresponding reduction in Arctic sea ice, has been having on winter across the mid-latitudes where most of us live.

This time series shows the Arctic sea ice extent in millions of square kilometers over the past roughly 1,500 years. Taken from the 2017 issue of NOAA’s Arctic Report Card, scientists report on a body of paleoclimate research that shows that the extent and rate of sea ice decline in the Arctic is unprecedented over at least the past 1,500 years. Climate.gov image adapted from Figure 3 in “Paleoceanographic Perspectives on Arctic Ocean Change” in the 2017 Arctic Report Card. Original data from Kinnard et al., 2011.

The debate arose because, while winters have in general warmed during the last century, some regions have shown a weak cooling trend for certain periods. A cooling trend, from around 1990 through 2013 in landmasses across the mid-latitudes, has been noted in previous research (Cohen et al 2014). It seems these cooling trends have generally weakened or disappeared when data has been updated to the present, but recent winters with bouts of record cold keep the debate alive.

The answer to the debate could have large ramifications for our ability to forecast the winter year in and year out. And I know that is something that concerns all of you, based upon the plethora of winter-related comments you leave on our posts.

In new research from across the pond in England, a team of scientists found that even though a lack of sea ice occurs at the same time as cold mid-latitude winters, it doesn’t cause those cold mid-latitude winters. In scientific jargon-ese, “correlation does NOT mean causation.” The real driver, they say, is an atmospheric circulation pattern across higher latitudes, which drives both low amounts of sea ice and the spilling of cold air into the mid-latitudes. But in order to come to that conclusion, the scientists first had to untangle those multiple, messy climate influencers.

Untangling the options
The difficulty in most investigations of our planet is that a lot of things are influencing the climate all at the same time. It’s like getting your Christmas lights out of the attic and finding two strands of lights hopelessly intertwined. This research, led by Dr. Russell Blackport, first had to untangle those Arctic “lights” in order to see which one is the strand that is “working”, or influencing our mid-latitude winters.

Let’s briefly describe the two influencers at play here and how they could impact mid-latitude winters. First up, a below-average amount of Arctic sea ice. Sea ice is both a reflector and an insulator. When bright, white ice is replaced with the dark ocean in the summer and fall, the surface absorbs more sunlight, and the warmer ocean then warms and moisten the atmosphere above it. This boost of heat and moisture, the thinking goes, can then change the larger atmospheric patterns above the Arctic in winter, which can be the first in a cascade of atmospheric dominos that could potentially lead to impacts across the mid-latitudes.

The second potential influencer is changes in the atmospheric circulation. Circulation changes near the Arctic, even caused by changes as far away as the Tropics, can drive warm moist air into the Arctic and melt/slow the growth of sea ice (Baxter et al. 2019, Clark and Lee, 2019). These same circulation changes could also be simultaneously associated with colder weather in the mid-latitudes.

The critical difference between these two options is the direction heat flows at the surface.

Anomalous “bottom up” heat flows (from ocean to atmosphere) would indicate that a lack of sea ice was driving the weather patterns; anomalous “top-down” heat flows would mean the atmosphere was running the show. These opposite heat flow patterns gave the scientists a way of testing whether, during winter, the amount of sea ice is driving the atmosphere or the atmosphere is driving the amount of sea ice.

Onto the pretty picture phase.
With a mechanism for sorting out the key players from the chaotic atmosphere determined, it was time for the authors to turn their attention to the full picture. The scientists ran two climate models many times to get a large sample of hypothetical winters, and also examined a dataset of historical observations. These representations of the atmosphere, specifically the sea level pressure and surface air temperature, were then linked to sea ice area in the Chukchi-Bering Sea to create a picture of the atmosphere during high and low amounts of sea ice.

How winter surface temperature (colors) and sea level pressure (contour lines) anomalies related to sea ice area in the Chukchi-Bering Sea. Reds refer to warmer temperatures and blues refer to colder temperatures. Solid contours represent positive sea level pressure values and dashed contours represent negative anomalies. Anomalous winds flow counterclockwise around negative contours and clockwise around positive contours. When Arctic sea ice is reduced, and warm surface temperature anomalies are present over the Arctic, there are corresponding cold anomalies across North America. Climate.gov image adapted from Blackport et al. 2019, based on ERA-Interim observational reanalysis data.

From the figures, it was very clear that a warm Arctic is strongly linked with cold North American winters via an anomalous cyclonic (counter-clockwise winds) pattern to the west of the Chukchi-Bering Sea and an anti-cyclonic (clockwise winds) pattern to the east. These opposing pressure anomaly patterns result in warmer, moist air being drawn over the Chukchi-Bering Sea and, at the same time, colder Arctic air being funneled south over North America.

But the really interesting thing is what happened when they broke down these winters into just those that corresponded to either sea ice driving the atmosphere (i.e. those with “bottom-up” heat flows) or the atmosphere driving the sea ice (“top-down” heat flows), as determined by the sorting mechanism mentioned earlier.

During winters when sea ice is pushing the atmosphere around, there simply is no cooling over North America, despite there being warming over the Chukchi-Bering Sea. But during winters when the atmosphere is in the driver’s seat, the pattern very closely resembles all of the winters, with both North American cooling and Arctic warming. The lack of a connection in the former sorting suggests that reduced sea ice has only a weak influence on the cold North American winters. More likely, changes in the atmospheric circulation are causing reduced sea ice AND the colder mid-latitude winters.

Winter surface temperature (colors) and sea level pressure (contours) anomalies related to the sea ice area in the Chukchi-Bering Sea using the ERA-Interim observational reanalysis dataset. Reds refer to warmer temperatures and blues refer to colder temperatures. Solid contours represent positive sea level pressure values and dashed contours represent negative. Anomalous winds flow counterclockwise around negative contours and clockwise around positive contours. The top image shows the relationship during all winters. The bottom left image shows the relationship for only those winters where sea ice is driving the atmosphere. The bottom right image shows the relationship for only those winters when the atmosphere is driving the sea ice. The patterns between all winters (top) and when the atmosphere drives the sea ice (bottom right) are the most similar, indicating that the atmosphere is driving cold mid-latitude winters, not the sea ice. Climate.gov image adapted from Blackport et al. 2019.

Forget seasons, what about monthly influences?
But what if sea ice’s influence is stronger on a monthly timescale than a seasonal one? Could a lack of sea ice on a monthly basis kickstart the atmosphere into a pattern that lasts for an entire season? To test this, the authors looked at what happened atmospherically if a month of reduced sea ice was preceded by atmospheric circulation changes or if the month of reduced sea ice came first (5). They came to the same conclusions. One month after reduced sea ice, there was little cooling in North America. Meanwhile, one month before reduced sea ice, there were changes in the atmospheric circulation consistent with cooling in North America, and warming in the Arctic.

The authors suggest that no matter how you cut it, reduced sea ice does not appear to be the main cause of recent cold North American winters. But what about…… THE FUTURE?!

Testing reduced sea ice in climate change scenarios
In one last test, the scientists took a climate model and reduced sea ice to the amounts expected in a world with 2°C of global warming (above the pre-industrial era). This gave the authors the advantage of directly assessing the cause of the impacts in the models (hint, did sea ice do it?), rather than trying to infer it. And once again, with even lower amounts of sea ice in the Chukchi-Bering Sea, a sea-ice driven atmosphere (that is, years in which there were anomalous “bottom-up” heat flows) did not result in colder winter temperatures in the mid-latitudes.

Does this research mean that the disappearance of all of that sea ice is having no influence on the climate whatsoever?
From Dr. Russell Blackport: “Our work suggests that sea ice has minimal influence on the weather in the mid-latitudes, however we still expect sea ice loss to have large impacts locally near where the sea ice is lost. The reduced sea ice and the large warming it causes are already having large impacts on local ecosystems and populations living in the far North. It is also likely that warming caused by sea ice loss near Greenland will contribute to the melting of the Greenland ice sheet, contributing to global sea level rise.”

Southwest #Colorado is getting hotter, experts say — The Durango Herald #ActOnClimate

Graphic credit: The Washington Post (Note: NOAA does not provide data for Alaska or Hawaii for this time period.)

From The Durango Herald (Bret Hauff):

Rising temperatures mean less ground water, changing plants

On Colorado’s Western Slope, the average temperature has increased at least 2.7 degrees since 1895, based on 123 years of weather records, NOAA scientists estimate.

Darrin Parmenter, director for the Colorado State University Extension Office in La Plata County, said the region’s average low temperature during the winter – a measure the United States Department of Agriculture calls “hardiness” – has increased significantly.

The hardiness statistic is measured on a scale of 1 to 13; the higher the number, the warmer the average low temperature. In the 1990s, Parmenter said Durango was classified in Zone 4. The city is now in Zone 6…

A Washington Post investigation and analysis of nationwide climate found Southwest Colorado is just south of one of the fastest-warming regions in the country. Grand Junction; Moab, Utah; and Montrose form the corners of a triangle of average annual temperature increase of more than 2 degrees Celsius, or 3.6 degrees Fahrenheit, since 1895.

Global climate data may be difficult for people outside the science community to appreciate, said Heidi Steltzer, professor of biology and environmental science at Fort Lewis College. Humans don’t experience time on the scales climate is measured…

Colorado has historically had shorter growing seasons because of extended snowpack, and high-snow winters in the 1930s through the 1960s typically led to a lot of rain in the summer, Steltzer said. The 2018-19 winter snowpack filled the San Juan Mountains and nourished the San Juan Basin much like it did in the mid-1900s.

Steltzer said she was excited for the opportunity to study the effects of late snow in the Alpine environment – she hadn’t seen snow like there was this spring in more than 20 years living in Colorado and studying the Rocky Mountains’ climate.

But what she saw took her by surprise. The snow melted in the high country sooner than expected, she said. Her field work in the San Juan Mountains this summer showed that plants at high elevations are “experiencing drought conditions” despite snow burying the region late into the spring.

Steltzer suspects that below-average rainfall and higher average temperatures this summer may have robbed the high country of valuable water storage and replenishment. Both can be attributed to a changing climate, she said…

Durango City Council committed earlier this year to reduce greenhouse gas emissions citywide by 80% and encourage the use of 100% renewable electricity in Durango by 2050. That includes transforming public energy usage for government buildings and activities while also crafting policies to encourage renewable electricity for residents and businesses.

FLC cut its greenhouse gas emissions by 58% from 2011 to 2018 and aims to be 100% carbon neutral by 2050.