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Recently Observed Climate Change and Implications for Future Climate Changes

Climate has changed in the past and will continue to change in the future. Climate change is a natural part of Earth's history. The issue is whether or not humans are significantly altering the natural progression of climate change, and if so, will these changes be detrimental to life on Earth, including human life? The basic argument made by the IPCC is that human emissions of greenhouse gases has been the major driver for recent observed changes in surface temperature. Quoting from section D.3 of the 2013 IPCC Summary for Policymakers: It is extrmely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. On this page we will examine the recent observed changes in temperture and climate as well as some of the impacts of those changes. You should realize that changes in temperature will be accompanied by climate changes like changes in sea level and changes in ice cover. These other climate changes really only serve as circumstantial evidence for the IPCC argument because they are expected to happen regardless of why the global average surface temperature may be changing. For example, if the recent warming of global average temperature is simply a natural cycle of climate change on Earth that is not influenced much by higher greenhouse gases, we still expect to see climate changes like reductions in glacial ice. After examining some of the recent observed changes in climate, we will take a look at what could happen in the future if some of the predictions made by current climate models are correct.

Please keep in mind that observed changes do not provide strong evidence for why the changes have happened. Sometimes it seems as if the IPCC starts with the assumption that all recent observed changes in climate (and even extreme weather events) are primarily the result of higher levels of greenhouse gases. However, we know that climates around the Earth have always changed with time regardless of human activity, and it is entirely possible that recent observed changes could be dominated by natural variability. It is one thing to say that observations show that global average air temperature has increased, Arctic sea ice has decreased, sea level has risen, and so forth, but entirely another thing to prove why these changes have happened. The IPCC reports go to great lengths to document observed changes in temperature, precipitation, sea level, and other items, calling them "indicators of climate change"; however, the fact that these changes are observed during a time when greenhouse gas levels are increasing is not proof that the climate changes were mainly caused by human emissions of greenhouse gases and not mainly the result of natural fluctuations in Earth's climate, which have produced large climate fluctuations thoughout the history of the Earth. A recurring message is that correlation does not prove cause and effect. For example, since 1980 we know that greenhouse gas concentrations in the atmosphere have increased and we also know that the global average surface air temperature has increased and that arctic sea ice has decreased, however the fact that these events are correlated with each other cannot be used as proof that one caused the other. Unless otherwise noted, the observed changes presented below were taken from the 2013 IPCC report titled Climate Change 2013: The Physical Science Basis. The full report is 1552 pages.

Attributing Observed Climate Changes to Human Activities

The most recent IPCC report (2013) is now more forceful in its statement concerning the anthropogenic influence on observed climate changes: It is extrmely likely that human influence has been the dominant cause of the obseved warming since the mid-20th century. According to the IPCC, extremely likely means over 95% certain. The 2007 report used the term "very likely," which means over 90% certain. Given that the global average temperature has not increased since about 2000, which was not predicted by any of the IPCC climate models, it is somewhat surprising that confidence in the above statement has increased since the last report. The new assessment is said to consider longer and improved records and observations of climate change, as well as improvements in climate model simulations. Instructor's note: I wonder if they are putting too much faith in the ability of climate models.

Beside the International IPCC report, there are reports by US government agencies that claim there are climate change impacts that are already easily observable (e.g., see this EPA page on climate change indicators). In many of these reports, the reader is lead to believe, either explicitly or implicitly, that the climate changes mentioned are largely the result of global warming caused by human additions of greenhouse gases. First, it can be quite difficult to prove that climate has changed significantly given our incomplete knowledge of past climates and our incomplete understanding of how the climate system operates. Then on top of that we would need to prove that the climate changes were significantly influenced by higher levels of greenhouse gases. Most of the climate changes discussed in the EPA reports would be considered negative or bad effects of climate changes and end up being discussed in context of endangered species, forest resources, water availability, disaster planning, and the like. Often these possible bad effects of climate change are given as reasons to guide policy on greenhouse gas emissions in spite of the lack of scientific proof connecting them with increases in greenhouse gases.

On the other hand, there are many climate scientists who do not fully agree with the reports published by government agencies. It is important to realize that there is nowhere near a scientific consensus that fully agrees with the conclusions and predictions of future climate change made within the IPCC report. A skeptical view on some of the recent climate change indicators mentioned by the US EPA and attributing these changes to greenhouse gases is provied in this short article, Climate Change Impacts In The USA are Already (Not) Happening. A more comprehensive report from the Nongovernmental International Panel on Climate Change (NIPCC), Climate Change Reconsidered II: Physical Science has been updated in 2013. The full report is over 1200 pages and was written by a team of over 50 international climate scientists. There is also a shorter "Summary for Policymakers" similar to that produced by the IPCC. Quoting the first two paragraphs from the NIPCC Summary for Policymakers:

      "The [NIPCC] is an international panel of scientists and and scholars who came together to understand the causes and consequences of climate change. NIPCC has no formal attachment to or sponsorship from any government or governmental agency. It is wholly independent of political pressures and influences and therefore is not predisposed to produce politically motivated conclusions or policy recommendations.
      NIPCC seeks to objectively analyze and interpret data and facts without conforming to any specific agenda. This organizational structure and purpose stand in contrast to those of the United Nations’ Intergovernmental Panel on Climate Change (IPCC), which is government-sponsored, politically motivated, and predisposed to believing that climate change is a problem in need of a U.N. solution."

Model Projections of Future Climate Changes

We should expect that climate will continue to change in the future regardless of whether or not the changes are natural or largely caused by human emissions of greenhouse gases. The following list of items was taken from the 2013 IPCC reports. The models predict continued warming primarily caused by greenhouse gas increases. Because this list is based on climate model projections, these changes are by no means certain to happen.

Potential Impacts of Climate Change / Impact Studies

Impact studies are done to try to understand how humans and other life will be affected by climate changes. This is really the ultimate question to answer. Unfortunately, we are not very good at predicting future climate changes, which makes impact studies uncertain. Most impact studies today are performed by models that first read as input the climate changes predicted by a climate model. Thus, if climate model projections for the future climate in a given ecosystem are wrong, then the projected impacts on that ecosystem will be wrong. Given the uncertainty in climate model projections, it is probably a good idea to perform impact studies on a whole range of possible future climates before deciding any long-term policies. Also keep in mind that even if we know for sure how the climate will change within a given ecosystem, it is still difficult to understand and predict how life within that ecosystem will adapt. Below is a list of some of the considerations within impact studies:

Please also read over this WORD document defining Impact Studies and Outlining possible consequnces of Global Warming. The figures and links below are from the EPA's pages on the impacts of climate change. As you might expect, this government website is biased toward possible negative impacts of climate changes resulting from human emissions of greenhouse gases.

[Potential Climate Change Impacts]


Health Impacts

Water Resources Impacts

Forest Impacts

Coastal Areas

Species and Natural Areas

Agriculture Impacts

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