Global Warming is About More Than Carbon Dioxide Alone

In my recent blog post on Global Warming and Uncertainty, which you can read here, I explained that, although carbon dioxide (CO2) is the main driver behind human-induced global warming, feedbacks will ultimately determine how much the global temperature increases. If you are unfamiliar with the concept of feedback and how it relates to global warming, I suggest you read that earlier blog before continuing here.

Global Warming CO2 #3 2016-07-07Many climate models show that, although the effect of a doubling of CO2 concentrations in the atmosphere from the pre-industrial level of 280 parts per million (ppm) to 560 ppm will cause a temperature increase of somewhere between 3.5 and 8.1 degrees F, only a portion of that (about 2-3 degrees F) can be directly attributed to CO2 itself. The extra temperature rise is due to how the models calculate feedback. Those who say that temperatures will rise by less than 2-3 degrees F are arguing that Earth’s climate engine has negative feedbacks built into it which will prevent the initial effects of CO2 warming from being amplified. At this point, it is very difficult for either side to “prove” whether the feedbacks will be positive, leading to more warming, or negative, leading to less warming. So we are left with hypotheses, or educated guesses. I have studied the literature carefully, and I personally believe that positive feedbacks will rule the roost, leading to an amplified warming. Let me give you some of my reasons.

The primary feedback from an initial warming caused by an increase in CO2 is increased evaporation from the oceans, which adds water vapor (H2O) to the atmosphere. But water vapor is a greenhouse gas, so this leads to more warming. The extent of this warming is unclear, primarily because water vapor gathers in the form of clouds, and clouds themselves have an ambiguous effect in terms of feedback. On the one hand, since their tops are white, clouds tend to reflect solar radiation back to space. This is a negative feedback, preventing warming of the atmosphere. On the other hand, clouds hold heat in near Earth’s surface, especially at night, leading to more warming – a positive feedback. Those who expect that the negative feedback from clouds will prevail are making a very large assumption, particularly since we already know that the presence of water vapor in the atmosphere leads to increased warming. So while I am not denying that an element of negative feedback exists, I am just not convinced that it will equal or exceed the other positive elements.

The other major feedbacks, similar to the case of clouds, involve changing color – this time of Earth’s surface itself. Since the initial effect of CO2 is warming, we are witnessing the retreat of glaciers, sea ice and snowpacks, particularly in the northern hemisphere. This leaves a darker surface, both at sea (dark blue) and on land (mostly green and brown). Replacement of white surface with dark water and land reduces the amount of solar radiation that reflects back into space, and causes a great deal more heat to be absorbed on Earth’s surface. I think it is hard to overstate the importance of this phenomenon, especially since it played such an important role at both ends of previous ice ages. As more snow piled up due to initial cooling caused by changes in Earth’s orbit, the colder Earth became, leading to ice ages. As snow receded near the end of the ice ages, more dark surface was exposed to the sun, allowing for an acceleration of the warming that led to the climate we have today.

So there you have it. If the doubling of CO2 itself without feedbacks is expected to increase global temperatures by about 2-3 degrees F from pre-industrial levels by 2100, it looks to me like we can expect an overall warming of greater than 3 degrees. Some climate models put that number at about 8.1 degrees F, a warming that would completely transform Earth in ways that can only be described as catastrophic. But then again, perhaps the positive feedbacks, even though they do rule the roost, will not lead to that much warming. In fact, up until now climate models have tended to over-predict the increase in global temperatures by about 30-40 percent, possibly because they do not sufficiently account for some negative feedback. Given all these factors, my best estimate for a doubling of CO2 by 2100 is about 4 degrees F. This will mean a climate warmer than any Earth has seen in the last 7 million years, a period far longer than humans have been around. At a minimum, the challenges our descendants will face from this will be enormous. But there is still time to take action to prevent a doubling of CO2 from occurring. That presents an enormous challenge to US.

Tom Blaine is an Associate Professor with OSU Extension, Community Development. Feel free to contact him to present a global warming update to your group.

Global Warming and Uncertainty

In a previous blog post, I wrote an update on global climate change. One of the things you may notice now is the title of the current piece is on global warming, as opposed to global climate change. It has become the trend in recent years to replace the former with the latter, but I am going against that trend for the moment to make a point, and hopefully to get the reader to understand why there is so much uncertainty on this topic.

Greenhouse Effect 2016-01-28It was in the middle of the 19th century when scientists first discovered in the laboratory that carbon dioxide physically blocks the movement of infrared energy (think: heat). Scientists also pointed out that industrialization leads to higher concentrations of CO2 in the atmosphere. Within a hundred years (by the 1950s) scientists were getting very good at obtaining precise measures of atmospheric CO2 concentrations, and these measurements have been showing a constant increase every year since then. This is the evidence upon which the concern about global warming exists. If CO2 concentrations continue to increase due to our use of fossil fuels, this means that more heat gets trapped in the atmosphere, and therefore global temperatures rise (this is referred to as the greenhouse effect).

Now we get back to the difference between global warming and global climate change. If temperatures rise because of an increase in atmospheric CO2, that is not the end of the story. Earth’s atmosphere is full of “feedback mechanisms.” Feedback occurs when you have a change in a system that then causes something else to change. Imagine inside your home. You have a thermostat. In winter, you set the thermostat to “heat.” If the temperature in the house falls due to cold weather outside, the thermostat causes the heat to turn on, and the temperature rises. This is an example of “negative” feedback. “Positive” feedback occurs when a change in the system causes the initial change to be accented, so that the final status is more extreme than after the first round. Think about what happens when an electric guitarist starts playing very close to a speaker. The sound from the speaker adds to what initially goes through the amplifier, and so the volume skyrockets – ouch, it hurts my ears just thinking about it.

So the big question in global warming research is whether Earth’s climate system is dominated by positive or negative feedbacks. The effects of a doubling of CO2 concentrations alone may be in the neighborhood of 2-3 degrees F. But the real question is “then what?” That is one of the reasons why we have seen the shift from a discussion of global warming to global climate change.

Global Warming - Uncertainty clouds 2016-01-28One result of higher temperatures is more evaporation from the oceans, which puts more water vapor into the atmosphere. But water vapor is a greenhouse gas also. This feedback therefore would appear to be positive, and would lead to even more warming. But more water vapor means more clouds. And the effect of clouds on temperatures and climate is extremely complex. On the one hand, clouds tend to reflect sunlight high in the atmosphere, and therefore cause global cooling (a negative feedback). On the other hand, clouds trap heat in the lower atmosphere, especially at night (a positive feedback).

Scientists are now working to determine the kinds of climate change that are occurring or will soon occur as Earth’s temperatures increase due to higher concentrations of CO2 in the atmosphere. Much of this work is related to the kinds of feedbacks that are present in Earth’s climate engine. I understand that certain feedbacks are positive while others are negative, but it is hard for me to believe that the net feedback can be anything but positive. That is, it seems to me that the ultimate effect of a doubling of CO2 will lead to an increase in Earth’s temperature of more than 3 degrees F. More on why that is the case in my next blog entry.

(Submitted by Thomas W. Blaine, PhD, Associate Professor)