Jay Gulledge's blog
The cold weather continues across much of the Unites States, Europe, and central Asia as the Arctic Oscillation remains in a strong “negative” state, forcing cold Arctic air down to the mid-latitudes. A couple of weeks ago I explained why more frequent heavy snowfall events could be a consequence of global warming for mid-latitude areas near large bodies of water, like Washington, D.C., and Syracuse, New York (see figure).
|The average amount of annual snowfall has been increasing in Syracuse, New York, for most of the past century. (SOURCE: Increasing Great Lake–Effect Snowfall during the Twentieth Century: A Regional Response to Global Warming? Journal of Climate vol. 16, pp. 3535-3342, Figure 1)|
On January 31, I noticed a forecast for lake-effect snowfall around the Great Lakes on Weather.com: “Lake-effect snows are also possible near the central and western Great Lakes today and tonight.”
On December 19, Washington, D.C. was buried by two feet of snow, setting a new record for snowfall during the entire month of December and paralyzing the city for three days. As my neighbor and I shoveled out from the storm, he stopped for a moment, grinned, and asked, “So what happened to global warming?” Boy was he surprised when I said, “Glad you asked,” and launched into a 15-minute oratory on why global warming might mean more, not less, extreme snowfall for some parts of the world.
Before continuing, I need to reiterate that no single weather event can be attributed to global warming. So the question here is not, “What caused the heavy snowfall on December 19?” The question is, “Is heavy snowfall or unusually cold weather inconsistent with global warming?”
You need two things to create heavy snowfall: moist air and cold air. The two generally don’t occur in the same air mass because cold air can’t hold much moisture. So you need two air masses, one that is warm and moist and one that is cold and dry, to collide with each other. That is exactly what happened over the Mid-Atlantic region on December 19.
This condition is not only consistent with global warming, but it can be expected to occur more frequently in certain places as a direct result of global warming. It takes warmth to generate moist air. First, you need warmth to evaporate enough water from lakes or oceans to generate a massive snowstorm. Second, you need warm air to keep the water vapor aloft so that it doesn’t rain out before it finds a cold air mass to collide with. When I asked weatherman Joe Witte where the moisture that ended up in my snow shovel came from, he said, “Some of the moisture came out of the Gulf of Mexico AND some from the warm Atlantic ocean with the VERY warm (70s!) Gulf Stream along the East coast acting as a hot plate for evaporation of moisture into the cold dry air.”
|(SOURCE: NOAA polar-orbiting satellite data compiled by Rutgers University Coastal Ocean Observation Lab)|
Although the past few weeks have been very cold in the eastern United States, Joe pointed me to NOAA satellite measurements that found sea surface temperatures in the Gulf of Mexico and the Atlantic Ocean to be 1 to 3 °F warmer than normal during the week before the big snowstorm hit (see figures above). There is strong scientific evidence showing that, on average, the oceans are warmer today than they were a century ago because of human-induced global warming. So the warm ocean temperatures that fed the heavy snowfall are consistent with global warming. In fact, because of global warming, we should expect such conditions to be more common today than in the past and even more common in the future as warming continues.
So where did the cold, dry air come from? Global warming is about changes in long-term averages and not about single events; it does not mean an end to cold weather. Instead, it means that cold weather will become less frequent and hot weather more frequent when averaged over decades. In fact, both of these trends have been observed over the past 50 years in the United States and globally. So, even with global warming we will have cold winters, just fewer of them. It is also important to remember that a cold winter here doesn’t mean a cold winter everywhere. In fact, many parts of the world, including the Arctic and the tropics, are having an unusually warm winter. The current cold snap is concentrated in the mid-latitudes of the northern hemisphere, and there will always be the potential for cold Arctic air masses to visit the mid-latitudes from time to time.
The current cold snap is related to a known weather pattern called the Arctic Oscillation. When the Arctic Oscillation switches between “positive” and “negative” states, it simply shifts heat between the Arctic and the mid-latitudes. Scientists call this kind of pattern “internal variability,” and it does not change the total amount of heat in the climate system. Internal variability can create strong differences in the weather from year to year and place to place, but these shifts average out to zero net climate change over decades. Only a net change in the total amount of heat in the climate system can change the long-term average climate, and that is the nature of global warming.
When the mid-latitudes get periodic blasts of cold Arctic air, global warming makes it more likely that the cold air from up north will collide with moist, warm air from down south, creating more heavy snowfall events in mid-latitude areas near large bodies of water. A similar phenomenon is affecting the Great Lakes region. Syracuse, New York is one of the snowiest places in the country, but it and other areas around the Great Lakes are getting even snowier! Because the Great Lakes are getting warmer, they are icing over later and melting earlier than they used to. Without the ice, water can evaporate and enter the atmosphere over the lakes later in the fall and earlier in the spring. When winds blow this moist air over the land where temperatures are lower, we get the famous “lake effect” snow. With more open water during the winter, more lake effect snow is falling.
These are the cold facts of global warming.
Jay Gulledge is Senior Scientist and Program Manager for Science & Impacts
This Thanksgiving, I’m thankful we base policy decisions on peer-reviewed science instead of emails!
The kerfuffle over email correspondence hacked from a server at the University of East Anglia’s Climatic Research Unit is making climate change deniers giddy. But just like all the other non-smoking guns they’ve waived around over the years, this “mushroom cloud” will soon blow away. Nothing has come to light that undermines scientific assessments of the climate system, which are firmly anchored in peer-reviewed scientific publications, not emails.
Some of the past “smoking guns” that were supposed to put the theory of human-induced climate change in an early grave are among the hot topics flying around in the hacked emails. One was a paper by Soon and Baliunas published in a peer-reviewed journal called Climate Research in 2003. That paper was supposed to put to rest the conclusion of the 2001 IPCC report that the late 20th century was warmer than any previous period in the past millennium, but it was quickly and thoroughly refuted in the peer-reviewed literature (not in emails). Another was a 2005 paper by McIntyre and McKitrick in an often-not-peer-reviewed journal called Energy & Environment. This paper had the same goal as the first one, but it too was rebutted in the peer-reviewed literature and in a report by the National Academy of Sciences (not in emails). In the emails, climate scientists complained about these papers and expressed frustration that they were published in spite of serious flaws. However, policymakers did not use these emails to help them determine America’s policy actions on climate change.
Much of the bickering in the emails boils down to scientists’ irritation over serious breaches of the normal peer review system to get denialist papers published (see here, here and here). The publisher of Climate Research (CR) admitted that the major conclusions of the paper by Soon and Baliunas “cannot be concluded convincingly from the evidence provided in the paper. CR should have requested appropriate revisions of the manuscript prior to publication.” The paper was so bad that three editors resigned in protest over its publication. The paper by McIntyre and McKitrick (2005) wasn’t peer reviewed at all and the editor of Energy & Environment openly stated, “I'm following my political agenda – a bit, anyway. But isn't that the right of the editor?” Scientists value the peer review process and they find it unfair and objectionable when they subject their own work to potential rejection while others circumvent this critical step in the scientific process to force low-quality research into the debate.
Luckily, none of this matters since the scientific assessments produced to inform policymakers about the science of climate change are based on peer-reviewed science publications, not on the opinions of individuals expressed in email correspondence. As happens in the normal scientific process, when the occasional bad paper slips through the peer review cracks it gets refuted through subsequent scrutiny in the peer-review literature. In the end, what may be said in emails doesn’t matter; the scientific peer-review process will prevail.
Jay Gulledge is Senior Scientist and Program Manager for Science & Impacts
Scientists to Congress: You can argue about the politics all you want, but if you decide not to act on climate change, it won’t be because the science wasn’t strong enough.
In a letter sent today, a slew of scientific organizations, including the American Meteorological Society, American Geophysical Union, Crop Science Society of America, and American Chemical Society, informed the U.S. Senate that there is a strong scientific consensus that manmade greenhouse gases are changing the climate and that claims to the contrary are scientifically indefensible:
“Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver. These conclusions are based on multiple independent lines of evidence, and contrary assertions are inconsistent with an objective assessment of the vast body of peer-reviewed science.”
And they go further: “there is strong evidence that ongoing climate change will have broad impacts on society, including the global economy and on the environment.” They also say the United States will experience significant impacts; climate change isn’t just a problem for poor or developing countries:
It’s been difficult for average citizens to imagine what global warming means for them. After all, a few degrees of increase in the global mean temperature doesn’t seem too bad. But one consequence that has already been documented is an increase in intense downpours with longer dry periods in between. A recent report from the U.S. Global Change Research Program said,
“Changes in the geographical distribution of droughts and flooding have been complex. In some regions, there have been increases in the occurrences of both droughts and floods.” (p. 18) “The widespread trend toward more heavy downpours is expected to continue, with precipitation becoming less frequent but more intense.” (p. 24)
The historic drought that gripped the Southeast for the better part of two years and the severe flooding that hit the same region last week illustrate this pattern all too graphically.