Heat waves. Drought. Flooding. Cold spells. Wildfires. The climate system is changing before our very eyes, and there is no more glaring proof than the record-shattering loss of Arctic sea ice this summer.
The National Snow and Ice Data Center announced Wednesday that the sea ice covering the Arctic Ocean has smashed the previous record minimum extent set in 2007 by a staggering 18 percent. The impacts of rising temperatures and melting ice extend beyond the far north to us in the United States, as we are poised to feel the weather-related backlash.
The ice cover, only half of what it was only a few decades ago, is a stunning visual demonstration of the effects that increasing greenhouse gases, and resulting warming of the Earth, are having on the climate system.
Fossil fuels – such as oil, coal, and natural gas – are the main source of these added greenhouse gases, as they’re burned to provide the energy that heats our homes, lights our streets, and runs our vehicles. It now appears, however, that a gradual warming may not be the primary concern, as the gases may also fuel extreme weather around the world.
Since the fossil-fuel revolution after World War II, Arctic temperatures have increased at twice the global rate, illustrating a phenomenon called Arctic amplification. Thus, sea ice has melted at an unprecedented rate and is now caught in a vicious cycle known as the ice-albedo feedback: as sea ice retreats, sunshine that would have been reflected into space by the bright white ice is instead absorbed by the ocean, causing waters to warm and melt even more ice.
As temperatures over the Arctic Ocean fall with the approach of winter, the extra energy that was absorbed during summer must be released back into the atmosphere before the water can cool to freezing temperatures. Essentially, this loads the atmosphere with a new source of energy—one that affects weather patterns, both locally and on a larger scale. In spring, a similar phenomenon also occurs, but it involves snow cover on northern land areas. Snow has been melting progressively earlier each year; this past June and July it disappeared earlier than ever before. The underlying soil is then exposed to strong spring sun, which allows it to dry and warm earlier – contributing to Arctic amplification in summer months.
The difference in temperature between the Arctic and areas to the south is what drives the jet stream, a fast-moving river of air that encircles the northern hemisphere. As the Arctic warms faster, this temperature difference weakens, as does the west-to-east wind of the jet stream. Just as a river of water tends to meander when it reaches the gentle slopes of coastal plains, a weaker jet stream tends to have steeper north-south waves. Arctic amplification also stretches the northern tips of the waves farther northward, which favors further meandering. Meteorologists know that steeper waves are slower to shift westward.
The weather we experience at mid-latitudes is largely dictated by these waves in the jet stream. The slower the waves move, the longer the weather associated with them will persist. Essentially, “hot,” “dry,” “cold,” and “rainy” are all terms to describe very normal weather conditions. It’s only when those conditions persist in one area for too long that they are dubbed with the names of their extreme alter egos: heat waves, drought, cold spells, and floods. And these kinds of extreme events are precisely what we’ve seen more of in recent years.
Global warming now has a face and a fingerprint that directly touch each of our lives. Rather than just a gradual increase in temperature, we can recognize its influence in a shift toward more extreme weather events. A warmer atmosphere also means a moister atmosphere, so any given storm will have more moisture and energy to work with, increasing the chances of flooding or heavy snows. Arctic amplification adds another mechanism to the mix, making extreme weather more likely. The loss of ice and snow in the far north may load the dice for “stuck” weather patterns, compounding potential risks for our economy, our health, and our security.
Even though sea ice shattered its previous record minimum, we cannot yet predict what sort of weather this winter will bring to a particular region of the United States or northern hemisphere. We cannot pinpoint which part of the world will see frigid temperatures, heavy snowfall, or perhaps abnormally mild conditions next season.
It is clear, however, that more accurate advanced warning is needed to help vulnerable communities prepare for the extreme conditions in a warming world. We must continue to invest—both financially and intellectually—in research that expands observations, improves computer prediction, and delivers relevant information to decision-makers.
Because at this point, I can only say that I think it’s going to be a very interesting winter.
Jennifer Francis is a research professor at the Institute of Marine and Coastal Sciences, Rutgers University