Pope Francis, I am told, is trained in chemistry but he is not a climate scientist. This I have in common with him. I too have a degree in chemistry and am not a climate scientist. He and I cannot presume, therefore, to speak on climate from a position of scientific authority, but we trust the scientific method and understand its limitations and strengths, a perspective which is helpful. Otherwise we are not much different from everyone else. All of us depend on climate scientists to help us understand what is going on.
As a scientist who is not a climate scientist, here are my thoughts on climate change.
1. The science of weather and climate is extremely complicated.
Weather is the behavior of the atmosphere at a given location at a specific time. This is influenced by conditions of the land and water beneath it, as well as the weather in surrounding regions. Weather systems, therefore, are dynamic, non-linear (chaotic) interactions among enormous numbers of variables, few of which can be known with any certainty. It is small wonder weather forecasting is notoriously capricious. Yet it is surprisingly reliable. I recall as Hurricane Sandy was approaching the Eastern Seaboard, forecasters said over and over, we don't know what to expect because we have never seen a storm like this before, but the predictions were nonetheless uncannily accurate. Chaotic systems are not unpredictable. Recognizing the chaotic, fractal nature of our world gives us new insight, power, and understanding.
Climate is weather over longer periods of time and typically over wider regions. The region of interest may even be global and the time period as long as decades or centuries. But if weather is difficult to forecast, surely climate must be impossible. It turns out, however, that trends are easier to predict than the details, not simple, mind you, just less difficult. Climate systems such as El Nino, though, are notoriously difficult to forecast. This week I read reports that despite strong similarities between the 2015-16 and 1997-98 El Nino events, expert forecasters are refusing to make specific predictions.
All this is to emphasize that climate and weather are complicated. Computer modeling has a special fascination for me. Because the number of variables is so enormous, computer modeling even a few years ago was limited by memory costs and processing speed, but these boundaries seem to fall every year if not every month. Our computer models are now more accurate than ever, and often they are more disturbing. The latest predictions are more dire than the conservative estimates of just a few years ago. Yes, all this is complicated and much remains unknown, but the uncertainty is troubling not comforting. What we don't understand may be acceptable, ... probably not.
2. The science of man-made global warming is really simple.
(1) By contrast, the thermodynamics (physics) of green house gases (carbon dioxide, methane, water vapor, and others) has been well studied for over a century and is well understood. This has not been nor is it now in dispute. (2) The concentration of carbon dioxide and other green house gases in our atmosphere has been (and still is) steadily increasing. This is not in dispute. (3) The total heat content of the earth has steadily and dramatically increased since at least 1980. Yes it has been disputed that surface atmospheric temperatures have increased since 1998, but (a) in 1998 an abnormally strong El Nino caused heat transfer from the Pacific Ocean to the atmosphere, (b) even so ten of the hottest years on record have happened since 1998, (c) many high temperature records (and many fewer lower temperature records) have been broken since then, and (d) the steady rise in ocean temperatures since 1980 is undisputed. The earth is getting warmer, and the increase can be directly related to the increase in greenhouse gases in the atmosphere. Weather and climate predictions are actually harder than rocket science; the physics of global warming is not. It is straightforward.
3. The scientific consensus on climate change is crystal clear.
Consensus does not always guarantee truth, but scientific consensus is hard to come by and often it is associated with truth. It is the nature of science to be self-correcting. Individual scientists are not above error in judgment or interpretation, nor are they flawless even in groups, but science is truth seeking. The overwhelming consensus today is that man-made global warming and climate change is real, and it is serious. This consensus is demonstrable in at least two ways. First, more than 97% of those publishing in the area (as many as 99.9%) are in full agreement. Climate change is real, and human activity is the cause. Second, nearly every major scientific body in the world has issued such a statement. Scientific organizations are typically conservative about making such statements, so this is nearly unprecedented and significant. The notion that this is in debate is fabricated by the deniers.
4. The politics of climate science denial is all too familiar.
Here I have some personal experience. Not a lot, because I am a pediatrician, but when I was in medical school the surgeon general issued his statement about the health risks associated with cigarette smoking, and for decades big tobacco companies spent billions denying the science that was well established. Millions of people lost their lives unnecessarily as a result. Some of the same public relations firms are now involved in denying global warming and defending the fossil fuel industry. I am offended by this.
5. The consequences of climate change are already horrifyingly apparent.
So where do I start? The problem is that individual local crises are hard to connect to global "climate change." But honestly, these many disasters are becoming so severe and so commonplace, so "normal", that one can no longer imagine they are unrelated to what we have done to the earth and its climate. Moreover, the connections are often now becoming clearer.
A partial and less-than-systematic list of possible consequences would include: more powerful and dangerous hurricanes and tornadoes, drought and wildfire, intense rainstorms and flooding, deadly heat waves, bad air, allergies, asthma, infectious disease and food and waterborne illness outbreaks, ecosystem shifts and species die-gff, melting glaciers, early ice thaw, sea-level rise, and less fresh water.