Jesse Sartain Historical View
Historical View of Climate Change
Jesse Sartain Historical View By David Greenfield.
Many people don’t seem to realize that climate changes have been with us for a very long time. A common watershed mark is the beginning of the industrial era. If we look at pre-1780 we can see the following “drivers” or “forces” contributing to climate change: changes in the Earth’s orbit, changes in the Sun’s intensity, volcanic eruptions, changes in greenhouse gas concentrations and changes in ocean currents.
The Earth’s orbit does change, in terms of tilt and what are called “eccentricity” and “precession”. These affect the amount of sunlight striking the Earth’s surface. There are known fluctuations in the Sun’s intensity. These can cause both warming and cooling effects.
Solar activity affects both global warming and cooling. For example, reduced solar activity from the 1400s to the 1700s was a key factor in what came to be known as the “Little Ice Age”. This resulted in a cooling of North America, Europe and probably other parts of the globe.
Volcanoes are another “natural” cause of climate changes. It
is interesting to note that volcanoes emit aerosols and carbon dioxide. We don’t generally think of aerosols existing before aerosol cans.
The heating or cooling of the Earth can cause fluctuations in the heating or cooling of the Earth’s surface; this is the impetus for the current concern over emissions which are thought to contribute to the greenhouse gas effect. When global temperatures warm, carbon dioxide is released from the Earth’s oceans. This combined with changes to the Earth’s orbit trigger a warm or interglacial period, thereby increasing concentrations or levels of carbon dioxide. These increased levels amplify the warming effect by exacerbating the greenhouse effect.
If we look at the last 2,000 years we can conclude that the climate has been relatively stable. There have been three notable exceptions to this stability which scientists have labeled “the Medieval Climate Anomaly,” “the Little Ice Age” and “the Industrial Era.”
The so-called Medieval Anomaly is described as follows: between 900 and 1300 A.D. evidence suggests that Europe, Greenland and Asia experienced relative warmth. The exact magnitude, geographical regions and timing of these warming periods are uncertain. It is documented that the American West experienced very dry conditions during this time.
The Little Ice Age, as it was called, was sort of a misnomer, because it was not a true “Ice Age.” Major ice sheets did not develop, however, between 1500 and 1850, the average temperature of the Earth was possibly up to 2 degrees (Fahrenheit) colder than today, varying by region.
The Industrial Era is the anomaly we look at most closely today because another warming period has ensued over the last 100 years, coinciding with a substantial increase in emissions from human activity. According to the Environmental Protection Agency, starting around 1750, human activity began to add substantially to heat trapping greenhouse gases in the Earth’s atmosphere. Both the burning of fossil fuels and an increase in the Earth’s biomass, for example, has resulted in emissions of aerosols. These aerosols absorb and emit heat and simultaneously reflect light. The addition of greenhouse gases and aerosols in to the Earth’s atmosphere has created observed climate changes. Here are some of our current understandings as to why these changes have occurred:
First of all, land cover and land use change are cited. Changes in land surface can be just as important as changes to the atmosphere because of how much they affect the reflectivity of solar rays. Processes such as deforestation, reforestation, desertification and urbanization often contribute to changes in climate temperature, wind and precipitation. Changes in land cover and land use can also affect the amount of carbon dioxide taken up or released by the land surface. A whole science surrounding “carbon sequestration” has developed around these phenomena.
What is in store for the future? Greenhouse gas concentrations are expected to increase during the next century unless greenhouse gas emissions decrease significantly from present levels. These gas concentrations are expected to raise the Earth’s temperature, influence precipitation and create storm patterns which may raise sea levels. It is speculated that future climate changes will depend on the following: Whether there will be a continued increase in the production of greenhouse gases and aerosols. How strongly features of our climate respond to these concentrations. And lastly, how much the climate will vary due to natural influences such as the Sun’s intensity or volcanic activity. Another consideration is what is called the Earth’s “internal variability,” referring to random changes in the circulation of the Earth’s atmosphere and oceans.
We are currently producing virtual models of possible changes to the Earth’s atmosphere on computers. Climatologist calls these GCMs or General Circulation Models. According to the IPCC (Intergovernmental Panel on Climate Change) these models are thought to be “extremely important tools for simulating and understanding climate, and there is considerable confidence that they are able to provide credible quantitative estimates of future climate change, particularly at larger scales.
The entire subject of global warming is polarized between nations, political parties and economic interests. Even in the scientific community there is disagreement about man’s impact on the environment and what constitutes good science.
Experts are even disagreeing on points as basic as establishing a means for measuring either the global mean temperature or what is referred to as AGW, Anthropogenic Global Warming.
As early as 1989, the United Nations claimed that we were on a ten year countdown towards a “tipping point” wherein the global mean temperature was likely to rise above a 2 degree increase above pre-industrial levels, in which case, there was nothing we could do to reverse the eventual cataclysmic effects of global warming. Of course that was 21 years ago.
Russian critics of the Kyoto Protocol, which calls for cuts in CO2 emissions, say that the theory underlying the pact lacks scientific basis. The American Physical Society reports: There is a considerable presence within the scientific community of people who do not agree with the IPCC conclusion that anthropogenic CO2 emissions are very probably likely to be primarily responsible for the global warming that has occurred since the Industrial Revolution. Other detractors state that the global mean surface temperature has not risen since 1998 and may have fallen since late 2001.