Geoscientists have a special obligation. We are the historians of Earth’s past, much as medical researchers have a responsibility regarding the understanding and honest communication of the functions of the human body and lawyers to understand and correctly interpret the law. Many of the tools we have established in our search for oil and gas, from plate tectonics to seismic stratigraphy, to study of paleoenvironments and paleontology, are being applied to understanding the geologic past in ways that document climate change.
To deny what is happening is also to ignore what our own profession and science is telling us and is a disservice to the public at large who depend on our expertise to help them make informed decisions.
The 20th century witnessed the greatest rise in living standards in human history, supported by the energy provided from fossil fuels. Now, however, we face the consequences; the great challenge of the 21st century, which may define how we live in the future: how to deal with a changing climate caused in large part by the emission of CO2 due to the burning of these fossil fuels.
The evidence for climate change comes from three main sources:
- The actual measurements taken from the ground, water, atmosphere and from space in recorded history
- The scientific principles behind the effects of solar radiation, the components in our atmosphere and an understanding of the applicable chemistry, physics and mathematics
- The geologic record of the past, which clearly demonstrates the changes in climate in the past and how to relate those changes with current processes
Careful measurements have documented the world temperature rise over the past century, particularly since 1950, with the overall rise of 1.3 degrees Celsius since 1880 (see figure 1). The rate of increase is accelerating and is now about 0.25 degrees per decade. The past three years (2015-17) have been the hottest ever recorded. However, temperature increases have not been uniform, north and south polar regions (above 60-degree latitude) have been warming at approximately twice the rate of tropical and temperate latitudes. The effects on both polar caps have been immense: as carefully monitored by NASA, the September (minimum ice period) north polar cap has lost 70 percent of its ice volume in the 1980-2016 period (figure 2). This would project to a September ice-free pole by around 2040. West Antarctica temperatures have actually risen at four times the planetary rate since 1950. The yearly ice loss from Antarctica has tripled in the 2007-17 period and the ice surrounding Antarctica reached an historic minimum in November 2016.
The rapid reduction in temperature differential between the poles and temperate and tropical latitudes, particularly in the northern hemisphere is weakening global circulation systems, such as the jet stream. This results in slower moving and stalled frontal and/or high-pressure systems and can produce prolonged record-breaking heat waves as seen this summer in East Asia and Northern Europe, and catastrophic levels of precipitation, such as we have seen in Houston last year. The number of extreme precipitation events on an annual basis doubled in the United States in the past 20 years compared with the last half of the 20th century. The warming of the polar regions, plus the increased temperature in higher altitude at lower latitudes is melting the ice caps and glaciers, contributing to an accelerating average sea-level rise of 1 millimeter per year from 1880-1920, 2 millimeters per year from 1920-1980 and 3 millimeters per year from 1980-2010.
Ocean temperatures have also increased and the thermal expansion of water is contributing to about a third of sea-level rise.
Increasing Green House Gases
The warming of the planet, particularly in the past 50 years is primarily due to increases in the atmosphere in heat trapping gasses. These gasses include carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Taking into account their heat-trapping properties, they account for 76 percent, 16 percent and 6 percent, respectively, of the greenhouse gases in the atmosphere (figure 3). Approximately 80 percent of CO2 released in the atmosphere (32 gigatons annually) comes directly from the combustion of fossil fuels, mostly from the combustion of coal, oil and natural gas. That amount has doubled in the past 50 years on an annual basis.
The largest proportion (42 percent) comes from the burning of coal, followed by oil at 34 percent and natural gas at 18 percent (see figure 4). Coal is far more CO2 intensive in emissions than oil, with gas being the cleanest hydrocarbon fuel. The burning of hydrocarbon fuels is estimated to account for only 20 percent of the GHG emissions of methane, whose rise is more closely correlated with overall human population and other activities and processes.
However, the melting of the permafrost accompanying the warming of the Arctic is beginning to cause massive methane emissions that are as yet unquantified, which may increase the methane warming effect. Most of the GHG emissions of N2O come from agriculture, with only 10 percent due to the burning of fossil fuels, so that increase is again more closely related to human population rise.
The largest factor, therefore, in climate change, is the level of CO2 in the atmosphere. From the fossil record we have multiple means of estimating the level of CO2 in the past (figure 5). Certain plants form differently depending upon CO2 level in the atmosphere. Chemical composition of shells of marine organisms also differ with CO2 atmospheric variation. From air bubbles in ice cores recovered from up to 800,000 years ago in the Antarctic, these variations have been tested and verified. Throughout most of the Mesozoic, a period with overwhelming geological evidence of warm climate and higher sea levels than the present, the CO2 level was around 800 parts per million. By the end of the Cretaceous, it had declined to about half that level before rising again in the Paleogene (65-30 million years ago) warming period, during which it rose back up to around 800 ppm. There is much geologic evidence that the CO2 rise and consequent Paleogene warming was due to increased vulcanism. About 30 million years ago, it again declined to about 400 ppm and at that time, along with a cooler climate, the Antarctic ice sheet formed. About 3 million years ago, a further decline is recorded, to below 300 ppm with evidence of the formation of the northern polar cap.
Since that time, as documented in detail by ice cores from the last 800,000 years (figure 6) the CO2 level has fluctuated between 180 and 300 ppm, with the lower number associated with a cold climate and extreme glaciation with sea level of about 100 meters below the present. We emerged from the last glaciation period about 12,000 years ago and the CO2 level has ranged from about 260 to 280 ppm through historic times until the late 19th century with the lower levels associated with “mini-ice ages” and the higher with the warmer periods.
The CO2 level began to rise as the industrial revolution gathered momentum and reached 300 ppm around 1900 and slowly rose to around 320 ppm by 1950. At that point, the explosion in economic activity and use of hydrocarbon fuels, especially oil, led by the United States, Europe and the Soviet Union pushed the level to 380 ppm by 2000. The industrialization of China, mainly fueled by coal, has been the most prominent factor in the rise in this century to the current level of 411 ppm. At the current increase of 2.7-3 ppm per year, consistent with the emission of 40 gigatons of CO2 emitted annually, a level of 500 ppm will be reached around 2050, a level not seen since the end of the Paleogene warming period, 30 million years ago.
Rising Sea Level
Based on the historical record and present-day observations and trends, by that time, the late summer north polar cap will be largely gone and the glaciers of the northern hemisphere, including Greenland, melted or well into the process of melting. The climate will have irrevocably changed in ways we are only now beginning to understand as the temperature differential between the poles and temperate and tropical latitudes will be further diminished. Sea level rise will be less than one meter by that time, but the rate of rise will be increasing. However, 90 percent of the planet’s ice above sea level is locked in the Antarctic ice sheet, protected by surrounding ice, and it is this melting that would cause the catastrophic sea level rise that would change the world as we know it. The fossil record indicates that it was when the CO2 level dropped significantly below 800 ppm that the Antarctic ice sheet began to form, and the achievable task facing mankind is to slow and then halt the rise in CO2 atmosphere content and find a way to gradually reduce it so that the CO2 level remains significantly below the 800 ppm level.
To deny the existence of global warming and climate change means to ignore or suspect that data provided by worldwide weather stations and NASA satellites has somehow been fabricated or altered. Looking at a half century of data, the trend and correlation between temperature and atmospheric CO2 content is obvious. The data from the Arctic and Antarctic is most troubling as it demonstrates an acceleration of the process beyond many of the earlier predictions.
There are natural climate variations documented in the ice cores of the past 800,000 years. These are likely due to eccentricities in the Earth’s orbit and variations in solar radiation. However, those natural variations over that time period caused CO2 levels to range from 180 ppm to a maximum of 300 ppm with cycle times of 50,000 to 100,000 years. We have had a 50-percent increase in CO2 from 280 to 411 ppm since 1880 – less than 150 years, with more than half of that increase in the past 40 years! This increase can be directly tied to the amount of CO2 emitted from the burning of fossil fuels and is clearly not “normal variation.”
(Editor’s Note: The opinions and positions stated here do not necessarily represent those of the EXPLORER editorial staff nor those of AAPG leadership or membership, but are the author’s own.)