Let me start this post by saying up front that, as a scientist, I believe that human activities over the past 200 years have resulted in a global warming trend that has been more rapid than any that we’ve seen in the paleoclimatological data to date. And I believe this current warming trend is setting us up for changes in our global climate that will continue way beyond our own lifetimes and will cause major disruptions in the lives of millions of people.
I try to avoid arguments on Facebook with climate change skeptics. Although sometimes I try to politely point out when their comment makes an incorrect assumption or draws an unsupported conclusion about climate science. And then someone else will often chime in trying to hijack science to support their view that climate change is a hoax or a conspiracy by ________ (fill in the blank with whichever liberal the person dislikes the most). I experienced a Facebook exchange just like this yesterday. Most of the time it’s people confusing weather with climate. Weather is what we experience day to day and differs from town to town. When we talk about climate, it’s on a global scale and trending over one year or thousands of years. Climate is driven by complex interactions of ocean currents and ocean temperatures with ambient air, resulting in the range of temperatures and range of precipitation experienced of over a given span of time at any given point around the world. That’s why I prefer to call it Climate Change. If I say global warming, someone will always point out that we just had one of the harshest winters in southeastern PA since the late 1970s.
The Facebook exchange started when one of my conservative friends posted a link to a climate-denier’s blog that discussed Antarctic sea ice levels increasing despite a warming global climate. Of course both the blogger and my friend took this sea ice observation as proof that global warming is a sham. So I took his bait and responded with the following analogy.
Trying to understand climate change is like watching a 5-hour long movie frame by frame. A human lifetime would equate to seeing one or two frames of that 5-hour movie. For a 21st century human to say that they do not see the climate changing is like viewing one or two frames of the movie and saying you don’t see a movie. To get an idea of what the movie is about, you’ve got to rewind through at least the previous hour. And that’s the case with climate change – you’ve got to look back at previous cycles of natural climate change to make sense of the rate of temperature change seen over the past 200 years since the start of intensively burning fossil fuels.
Then someone else tried to refute me by posting a graph showing ambient temperatures going back 10,000 years that were calculated from ice cores collected in Greenland. The graph came from an academic paper and was supposed to prove that it’s not as warm now as it has been for the past 10,000 years. Unfortunately, that individual was cherry picking data that was collected for an entirely different purpose than solving the global warming debate.
The graph in question was from a paper by Dr. Richard Alley, a widely respected glaciologist from Penn State. I had the opportunity to hear him lecture once when I was in grad school at Lehigh University, because he was a frequent collaborator with one of my professors. As esteemed as Alley is as a glaciologist, he would not claim to be a climatologist. So I looked up the abstract for the paper that this graph comes from, because I was curious about its context.
The title of the paper is, "The Younger Dryas cold interval as viewed from central Greenland." The Younger Dryas cold interval was a period from approximately 12,800 to 11,500 years ago in which the earth experienced a temporary period of cold, dry conditions. This 1300-year interval was at the tail end of the overall warming trend associated with the end of the most recent glacial period, which officially ended about 10,500 years ago. Alley would likely study the Younger Dryas to determine its effects on Greenland’s glaciers at that time. At the glacial maximum for the most recent glacial period (about 22,000 years ago), the glaciers had advanced about as far as Blue Mountain in eastern PA, Long Island, NY, and across many of the northernmost states in the Midwest. So the Younger Dryas period was a 1,300-year anomaly in the final 11,500 years of the most recent glacial period.
So in the big picture, yes, we are simply somewhere in the middle of one of several interglacial periods in the earth's 4.6 billion year history. But there is a preponderance of evidence indicating that carbon loading into the atmosphere appears to have accelerated the natural warming trend that we probably were already in. Indisputable proof doesn’t happen often in science, so we have to rely on the general conclusions of the overwhelming majority of climate scientists. Their climate models all vary to some extent, but most of them acknowledge the effect of man-made carbon tweaking the global climate and accelerating the rate of warming of our oceans and atmosphere.
The reason for concern is that the temperature increases we are seeing in our global climate over the past 200 years have been at a more rapid rate than the warming period from 22,000 to 10,500 years that ended the most recent glacial period. There is evidence to suggest that during the previous interglacial period, around 125,000 years ago, sea levels were 3-4 m higher than they are presently. So if our present interglacial period ultimately gets as warm as the one that peaked 125,000 years ago, we could be looking at sea levels rising 10-12 feet. Even a couple of feet over the next 100-200 years is going to displace millions of people.
And possibly an even more immediate concern is feeding the earth's 7 billion people when weather patterns shift and droughts become more prevalent in regions currently associated with agriculture. The eastern U.S. might get wetter as a result, but we've built on or paved much of our great agricultural soil in the east over the past 50 years. The threat to agriculture is one reason that the U.S. Department of Defense considers climate change a national security threat.
Of course, the explanation above, when offered on Facebook, was met with the usual accusations of academic dishonesty by the 95% of climate scientists who will say anything just to get more funding to perpetuate the hoax that the “Administration” wants people to believe. But at least our military is acknowledging the worst case scenario of a climate warming more rapidly than it appears to have over the past couple hundred thousand years. So I guess we need to modify that old adage that the two things to never discuss at a cocktail party are politics and religion. Regretfully, it seems that we need to add science to that list of taboo topics.