So What About Global Warming?

The Earth as seen from Apollo 17As a meteorologist, the most common question I get asked is, “Are you going to be on TV?” The second most common question I get asked is, “What do you think about global warming/climate change?” This is the question I want to write about here. And to be honest, my thoughts on global warming have gradually done pretty much a 180 over the past 10-15 years.

Back when I was in high school (1997-2001), I was convinced that anthropogenic (human-caused) global warming was a hoax. I honestly did not find the evidence to be compelling, and I thought natural variability better explained the data. I was so convinced that the case for anthropogenic global warming was a hoax that I wrote an 8-minute mostly-memorized oratory speech for Forensics in 1999, where I laid out what I thought was good evidence that it was a hoax. I even earned a perfect score with my speech at the State Forensics Tournament in Madison that year.

My opinion gradually started to change after I began graduate school for meteorology at Penn State University in 2005. Learning more and more about the fundamentals of atmospheric physics, along with seeing several more years of observations of the earth system come in, began to make me doubt my certainty that global warming was all due to natural variability. Now I am convinced that not only is global warming happening, but I think the evidence indicates that human beings are almost certainly at least partially causing it.

There certainly have been ups and downs in global average temperature throughout history that were entirely natural, but we are most certainly adding an additional component of warming onto the internal natural variability of the climate system. We know from measurements on Mauna Loa in Hawaii that the atmospheric concentration of carbon dioxide (CO2) has been steadily rising since measurements began in 1958 (at about 315 ppm) to today (about 402 ppm, or about a 30% increase in 60 years). The increase in atmospheric CO2 concentrations is due almost solely to human activities, such as the burning of fossil fuels (coal, oil, natural gas), deforestation, and the like.

Keeling Curve - CO2 concentrations observed at Mauna Loa

We also know from temperature records that the global average temperature has warmed about 1ºC (or about 2ºF) during the 100-150 years or so over which we’ve taken measurements, with a couple 20-30 year interruptions in that overall warming trend (more on that later).

Global mean temperature (1880-2014)

We know from physics that molecules of carbon dioxide and methane both quite effectively absorb and re-emit heat (longwave radiation, technically). The wavelengths of radiation at which they most effectively absorb and re-emit happens to correspond to bands that are known as “atmospheric windows” — wavelength bands to which the atmosphere is generally transparent, and through which the Earth vents much extra heat into space, to keep the Earth system in radiative balance. However, as we add more and more CO2 and methane to the atmosphere, those atmospheric windows become less transparent, and more heat is, in essence, trapped.

CO2 & H2O absorption

All else being equal, this has the effect of warming the Earth’s surface on average over a period of decades. To complicate matters there are several positive and negative feedback processes which amplify and counteract that basic, foundational signal. But, the basic effect is most certainly warming at the surface.

Back to the 20-30 year cooling interruptions we’ve seen periodically. Yes, the Earth cooled from the 1940s to 1970s, but that was from emitting lots of particulate pollution (coal dust, other things) into the atmosphere during a manufacturing boom, which had the effect of reflecting sunlight to space and cooling the planet. Eventually those particulates settled out of the atmosphere, and we started sending less of those pollutants up into the atmosphere (because we got tired of breathing in smog and dirty air), but the CO2 remained — its atmospheric lifetime is not a few weeks or months like many particulates, but rather hundreds of years. And the current hiatus we’ve seen since about 2000 is probably due to several factors, including somewhat less incoming radiation from the sun, a lot of heat getting stored in the deep ocean because of various ocean currents, and various large-scale, natural multi-decadal atmospheric climate oscillations that occur over large sections of the planet and interact with each other. That hiatus is not likely to last more than a few more years, as these natural climate oscillations flip back into their other modes. All those things would likely normally have cooled global average temperatures, were it not for the high and continually-increasing CO2 concentrations in the atmosphere, which are acting to warm temperatures at the surface. In the past 15 years those effects have essentially canceled each other out, but we’re still stuck with being on a plateau at the warmest we’ve been in the past 150 years.

In addition to the surface temperature record and the atmospheric CO2 concentration record, another powerful line of evidence is the decrease in Arctic sea ice extent. Ever since satellite observations of Arctic sea ice extent began in 1979, there have been annual ups and downs, but the overall trend from 1979-present has been a noticeable decrease:

Monthly sea ice extent, NH (1979-2015)

And current observations indicate that sea ice extent is nearly the lowest-ever this year:

Arctic sea ice timeseries

By itself this is not proof that global warming is happening, and while it is true that the Arctic Ocean has been ice-free occasionally in the past, long before the Industrial Revolution, decreasing Arctic sea-ice extent is definitely something we would expect to see in a warming world, along with steadily receding glaciers (which we also see around the world).

In summary, I believe that the evidence is now overwhelming that global warming: a) is really happening, and b) that it is at least partially caused by human activities. What to do in response to this evidence to attempt to mitigate or adapt to future climate change is another topic entirely, and that is where politics enters the discussion. Any mitigation/adaptation strategy has its pros and cons, but what is certain is that in the absence of significant reductions in global carbon emissions soon, the planet will continue to warm. That conclusion is not the result of some vast conspiracy, and it does not depend on the predictions from climate models (many of which have serious flaws) – instead, that is what basic physics tells us. My fellow political conservatives who still think global warming is a hoax would be well served to seriously consider the evidence. Instead of rejecting the scientific evidence because of a distaste for current policy proposals, it would be better to improve or develop better policy proposals in response to the scientific evidence.

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5 Responses to So What About Global Warming?

  1. GDS says:

    What proportion of meteorologists now think global warming is not, at least in part, due to human activity?

    Do you think some people whom you know to be climate change
    ‘nay-sayers’ will reconsider or even change their position/”belief” after reading your blog posting?


  2. Jack Doe says:


    Very nice write up. It is unfortunate that a topic that is complex and relies on advanced scientific understanding of nuanced processes has been politicized such that voters, who are not experts, have been included in a debate which is best had by people like yourself (now, not Jared of 1999). Because we’ve allowed (if not encouraged) this topic to be discussed in the same fashion as gun ownership, we’ve paralyzed our ability to adapt and overcome to a situation which, at best, will upset agriculture, alter property values, and negatively impact the poorest among us on the planet. At worst, we could see massive die offs of species and societal upheaval (I understand anthropologists believe environmental deterioration led to the downfall of the Mayan civilization, not to mention poor farming habits leading to the Dust Bowl and the largest internal refugee crisis our nation has ever faced).

    There are many among us on the planet that still believe that AIDS is curable by consuming human remains, that the earth is 6000 years old, and that immunizations cause autism. All of these things (disease, geology, genetics) are beyond what 99% of the public is trained to understand and shouldn’t be expected to understand. However, if we collectively lose our ability to listen to the scientific process in favor of long standing beliefs (not to mention political affiliations), we are failed as a civilization. It was just such failures that led to the death of President Garfield (it was the secondary infections due to doctors sticking their unwashed fingers into his bullet hole that killed him, all while a handful of younger doctors were being berated for suggesting sanitation may play a part in infection and that Europe had far fewer people dieing due to hand washing).

    Either way, kudos to coming around. I hope that the rest of our society can start treating other scientists in the same fashion which they treat MDs (i.e. if 95% of oncologists say you have cancer, you probably have cancer). Not to mention what seems to be the pretty easy to understand “…if you dump 100 million years worth of poop into any body of fluid, you are going cause something to happen in that body of fluid…” concept.

    • Jared says:

      Hi “Mr. Doe,” thanks for stopping by. I’m glad you appreciated my write-up. However, I have to disagree with your assessment of science and the public. I perceived elitism and condescension toward the public in your comment above (e.g., “99 percent of the public … shouldn’t be expected to understand [the science]”). I think it is unhelpful for scientists to have such attitudes toward the public. (Side note: That is especially true for scientists whose salaries ultimately come from taxpayer dollars!) Part of what I strive to do as a scientist is to educate the public about what I/we do in our research at NCAR (National Center for Atmospheric Research). We shouldn’t expect most of the public to have an expert’s understanding of any given discipline, true, but in my experience, many (most?) people are interested in learning if we patiently, clearly teach and explain the fundamentals of the science to them (while avoiding as much technical jargon as possible). That’s what I tried to do in this post, to explain the fundamental evidence in clear terms, while avoiding inflammatory and/or condescending language. The elitism that all too many scientists seem to display, whether wittingly or unwittingly, is off-putting to many, many people –including myself– and only fuels distrust of what the scientists say. How we convey a message is a critical component to the acceptance or rejection of that message. I readily confess that I don’t always do that well, but it’s an important goal to strive for.

      • Jack Doe says:

        Yeah, I probably worded that less than eloquently (long day, late at night, random blog posting). You’re right that the general populace (most of us) like science and is interested. Heck, even some folks who are ardent “conservatives” advocate for more science (see Newt Gingrich, Nixon, the Bush Family, etc.).

        The point I so haphazardly put to page, was that science, when politicized, distorts the public’s ability to understand it even more so than they would under other circumstances. The public shouldn’t be expected to make individual decisions on complicated scientific issues (which is exactly why we all see MDs when we’re ill and not trying to consume random fungus to try and cure a bacterial infection). Thankfully, the public can sometimes figure out when things are bad (i.e. acid rain, thalidomide, smog) and then act to fix them as a group. However, things that are less obvious in the short term (i.e. global warming) are much more difficult for the random guy to comprehend and thus work to change.

        I don’t think it has always been this way. There wasn’t (I don’t think) a 15 year long struggle to ban CFCs to fix the ozone layer, nor was there a 15 year long struggle to regulate SO2 & NOX to stop acid rain. My person opinion (which is worth less than a cup of coffee) is that there are a handful of people who benefit immensely off the status quo. Although they could just as easily profit off of a change of course, it is apparently a cost-benefit analysis which says lobbying against the scientific consensus and politicizing the topic is more profitable than any alternative (which, as a corporation, they 100% should be working towards their bottom line). Thing sad things is, the best financial interests of the minority do not converge with the best survivability interests of the rest of Earth’s population.

        I’d also argue that, although there is enough arrogance to go around, I do not know that advocating that our general populace should defer scientific issues from political debate and to instead rely on the scientific community to better guide the discussion. I mean, if a bunch of farmers or butchers go together and established a consensus that corn fed beef were lest healthy than grass fed beef, I’d probably have to listen to them since I have no idea. That doesn’t make those farmers and butchers “elite”, rather it makes them experts who know they know more than the general public and that the folks on the East and West Coast couldn’t identify a cow if they had to. Or, maybe a better comparison is, if every meteorologist says it’s going to rain tomorrow, they aren’t elite or being condescending to people doing a rain dance , they just know what the their stuff (and nobody accuses meteorologists of being in cahoots with the big rain jacket industry).

        Just my 0.02$. Thanks for the discussion!

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