Dr. Gosnold, chair of the UND department of geology and geological engineering, has analyzed temperature data from several hundred sites to document the Earth’s average temperature changes over the past 500 years. In the following Q&A with Office of University Relations writer Juan Miguel Pedraza, Gosnold talks about global warming, climate change, and what the current research about them signals for the future.

Q. We hear the terms “climate change” and “global warming” in the media seemingly used interchangeably; is there a difference between them?

A. Yes, there’s a difference, though they are, of course, related.

Climate change can be caused by a number of forcing mechanisms which basically change how much solar radiation reaches the planet’s surface or in how heat is redistributed after it arrives at the surface. Most of these mechanisms are natural and cannot be altered by human activity.

Global warming and global cooling are, indeed, climate change, but today we usually associate “global warming” with climate change caused by human activity.

Q. You say climate change is natural. How does it work?

A. We know that climate change can be caused by a number of forcing mechanisms, as I noted earlier. These are things that cause the climate to shift by changing the amount or intensity of solar radiation that falls on Earth’s surface or in how that radiation is redistributed. For, example the Milankovitch cycles: the eccentricity of Earth’s orbit changes over a 100,000-year cycle; the Earth’s axial tilt changes over 41,000-year cycles; and the precession of the Earth’s axis changes over a 23,000-year cycle. Together, these cycles cause slight changes in the amount of radiation falling on the planet, and these slight changes over time cause shifts in climate.

Q. Before we get too much farther along, can you define these terms?

A. Eccentricity is a measure of how circular the orbit of a planet or satellite is. In a perfectly circular orbit, the eccentricity is zero; elliptical orbits have eccentricities between 0 and 1, where 0 is a perfect circle and 1 is a straight line.

For the mathematically inclined, the eccentricity equation is e = (a2 – b2 )1/2/a, where a and b are the major and minor axes of the ellipse, respectively. Earth’s eccentricity has varied over time between 0.005 and 0.0607; right now, the eccentricity is 0.0167, or about 1:6, and has a period, or cycle, of about 100,000 years.
Precession is the “wobble” of the Earth as it spins on its axis. This wobbling motion does not affect the tilt angle, or axial tilt, of the Earth; however, it changes the direction in which the Earth is tilting. The wobble, or precession, completes its cycle about once every 23,000 years.
Axial tilt describes how far the Earth leans away from the vertical with respect to its orbital plane; if the Earth’s axis of spin did not tilt, there would be no seasonal changes because every place on the globe would receive the same amount of sunlight/darkness year-around, that is, 12 hours of daylight, 12 hours of night, with no variations from one month to the next.

Q. So let’s continue: as you were saying, there are “forcing factors” other than those you just described that propel climate change.

A. Yes, forcing factors other than solar radiation can be grouped into atmospheric composition, atmospheric circulation, and ocean circulation.

Humans can affect only one of these forcing factors: atmospheric composition.

We humans have increased the atmospheric content of greenhouse gases, primarily carbon dioxide, or CO2, by burning fossil fuels to a point where the heat balance of the planet has changed. Earth now is storing more heat than it was before anthropogenic, or human-produced, CO2 began accumulating in the atmosphere. The amount of CO2 in the atmosphere has increased by 27 percent (280 parts per million by volume [ppmv] to 380 ppmv) since the Industrial Revolution and the increase is a consequence of burning of fossil fuels.

An important point I would like to make is that H20 has a stronger effect than CO2 and that leads to a serious feedbackproblem.Global warming driven by all greenhouse gases has increased evaporation rates, and the amount of H2O in the atmosphere is increasing.

Q. Well, from what you’ve said about anthropogenic greenhouse gases and fossil fuel usage, we’re talking about how much we drive. We Americans are still the world’s largest—in terms of a single society—consumers of fossil fuels. More than half of the 22 million barrels of oil we consume daily is used in personal transportation. We continue to buy large vehicles in record numbers—the Ford F-150 full-size, half-ton pickup truck, for example, has been the best-selling vehicle in the U.S. for 21 years. Meanwhile, the U.S. Environmental Protection Agency reportes that fuel economy in American vehicles hit a 22-year low in 2002 and has not improved much since then.

A. Yes, internal combustion engines —transportation in general—are a major contributor to global warming.

A National Research Council report, commissioned by the National Academy of Sciences, was released this summer; it showed that, yes, global warming is real and humans are largely responsible, and the major factor is CO2 emission from burning fossil fuels. Auto and light truck emissions are increasing about 2 percent per year; of course, this constant annual rate of increase results in an exponential curve because every year’s 2 percent increase is built upon the previous year’s 2 percent increase, so you’re compounding the rate of increase.

It’s gotten scary; now, the major contributor to global greenhouse gases turns out to be the Third World. China and India are starting to make an impact with their huge populations and growing demand for oil. But that doesn’t diminish our role: the United States as a country is pretty much the leader in greenhouse gas emissions; the Europeans actually have reduced theirs since 1990 because their governments have taken it a lot more seriously than we have. They specifically have undertaken to reduce fossil fuel emissions.

Q. Please clarify what you said about the Third World’s role in global warming.

A. Demand for energy in the Third World is mostly for carbon-based fuel because that is the available resource and it’s the conventional resource; that’s what most economies are geared toward, petroleum, oil, gas, coal, and wood. China this year is using about 40 percent more crude oil than it did last year and its fleet of private cars is growing at about 20 percent per year.

Q. Any alternatives out there that would be practical, handy to access, and economical?

A. All alternatives (to fossil fuels) should be explored, but my favorite is geothermal; we have an enormous untapped resource that could replace much of the fossil fuel that we use, especially for space heating and cooling. According to current research, if the United States would step up to use ground-source heat pumps, we could reduce our electric power usage by 75 percent.

Q. So why haven’t we done it?

A. We haven’t done it because there are initial high-end costs, but the payback time for a geothermal or ground-source system is less than 5 years. Economics always plays a key role—that’s the first thing that people look at.

Q. Tell us how you became convinced that global warming is, indeed, real.

A. In 1989 I was working on a problem of heat flow, looking at how ground water in deep sedimentary basins moves heat under the ground. Many of the temperature gradient curves in my study showed a curious curvature toward warmer temps in the upper 100 meters of the boreholes.

As an aside, during a presentation of the research at the Fall Meeting of the American Geophysical Union, I noted that our long-held belief that the Earth’s mean (average) annual temp has been relatively constant for the past several millennia might not be true and that the climate might be changing. A senior U.S. Geological Survey (USGS) scientist who was in the audience sent me a letter and a copy of a paper he had published in Science with similar observations from deep boreholes in Alaska’s North Slope. He realized that we had discovered evidence for climate change and suggested that I look into all of my data.

Thanks to my previous research on geothermal resources, I had compiled a large database of subsurface temperature measurements in boreholes from North Dakota to Texas. UND geographer Paul Todhunter and I began a program to analyze those data to test a basic hypothesis: if greenhouse warming is occurring as general circulation models predict, we should see a systematic change in the amount of temperature change at the surface. The mid-continent data are especially suitable for this analysis for a variety of reasons that tend to suppress non-climate related signals. (Editor’s note: a general circulation model, or GCM, is a three-dimensional computer model of the global climate system; GCMs can simulate human-induced climate change.)

Also, our method has a significant advantage over the meteorological record due to the thermal damping of the climate signal. The low thermal diffusivity of the ground greatly reduces statistical uncertainty in the temperature time series. (Editor’s note: Basically, this means that Gosnold and Todhunter reached their conclusions by making observations across all of the many variations that occur from year to year, a process akin to getting the gist of a radio news broadcast through a lot of background noise or picking out a conversation at a crowded party.)

We found that warming has increased from south to north as predicted by the GCMs. We published the results in (the peer-reviewed journal) Global and Planetary Change; our paper was referenced in the recent National Research Council report on climate change.

Q. So what do you see happening as a consequence of global warming?

A. We’re going to see stronger storms, more property damage, greater threats to life and health, more extreme events. The National Oceanic and Atmospheric Administration has already documented a pattern of increasing occurrences of extreme weather events tied to global warming.

Longer-term, predictions are that we’ll see a rise in the level of the oceans, maybe as much as 7 meters, or about 23 feet. It’s uncertain how long the rise will take, but if some predictions on the rapid decay of the polar ice caps are correct, it could occur by the end of this century. Since more than 90 percent of world’s population lives close to sea level, the social and economic disaster resulting from that much of a sea level rise is almost incomprehensible.

We know that over the Earth’s history, climate change has generally occurred on the scale of millennia; but now, new evidence of rapidly melting ice in Greenland and Antarctica indicate that climate change has been scaled back to centuries instead of millennia.

I’m amazed that in the last year, so many things have come out about accelerated climate change. I’ve been surprised—one of the really startling things I have seen was a PBS video on global dimming which showed that there’s less sunshine because aerosols—various types of particles in the atmosphere—are reflecting solar energy back into space, so the amount of sunlight reaching the ground is 30 percent less today than in 1950.

The culprit is atmospheric pollution due to human activity. This may explain why climate researchers have had difficulty matching models of greenhouse warming with the actual rate of warming. The models did not include the reduction in solar radiation at ground level. Global dimming has retarded the rate of warming, and this tells us that without the aerosol pollution, Earth would have been warming at an even faster rate.

Q. Why are we seemingly unaware of this? Our collective problem-causing behavior doesn’t seem to be changing much.

A. First and foremost, what is happening in science is just not on the popular radar—changes on time scales of decades-to-centuries do not cause a sense of urgency for most people.
Second, there has been well-financed and effective campaign to spread misinformation about climate science. Things tend to be presented with a “two-sides” argument in most news media, and the misinformation campaign has taken great advantage of this.
The fact is, in the concept of Earth system science, we know that everything is related; energy from the sun drives our climate and always has. And we know that Earth’s average surface temperature is rising in contradiction of the trend expected from the Milankovitch cycles. We should be cooling and entering another glacial stage.

The paleoclimate record for the past 1000 years actually shows a slow cooling trend, but that trend reversed dramatically at the time of the Industrial Revolution.

Our view today is that the average temperatures of the first half of 2006 were the highest ever recorded for the continental United States and 9 of the 10 warmest years on record have occurred since 1995. The peer-reviewed scientific literature points to anthropogenic greenhouse gases as the cause of the temperature increase.