[Home] [Lectures] [Previous] [Next]

Recently Observed Climate Change and Implications for Possible 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 temperature 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.

It is interesting to note that over the last 120 years, there have been many "news" stories claiming that Earth's climate is changing and that those changes are going to be bad for humans and other life. Sometimes the predictions are for global warming, while other times the predictions are for a return to Ice Age conditions. Often there are experts or climate "scientists" attached to the claims. It seems to be part of human nature to extrapolate current trends to speculate or predict future doom. Please see A Brief History of Climate Panic and Crisis ... both Warming and Cooling for a list of historical examples.

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 ... for example, to prove that these changes would not have happened without the recent increase in greenhouse gases due to human activity. 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 did not increase significantly 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 projected climate changes 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. However, many people have determined that extreme action to reduce emissions is necessary to reduce the possibility that these harmful climate changes will take place. A precautionary principle can be applied. Climate models are considered by some to be the best predictive tools we have available. Even though there is uncertainty in the model predictions, according to the precautionary principle, we should not take the risk, and we should do whatever it takes to reduce greenhouse gas emissions in case the model predictions are correct.

Potential Impacts of Climate Change / Impact Studies

Impact studies are studies that deal with the question of how future climate change will affect humans and other natural ecosystems. This is actually the ultimate question that we would like to be able to answer in order to both prepare for the future and help decide if we need to aggressively reduce emissions. However, to answer the question correctly, we would first need to know with certainty how climate is going to change. In spite of all the research and climate models, our understanding and ability to predict how climate is going to change in the future, both from human and natural influcences, is quite poor. Also, keep in mind that the predictions of climate changes on regional scales (moderately-sized ecosystems) is much more uncertain and difficult than predicting global average changes, yet it is change on the regional scales that is most important for determining how life and human civilizations will be affected by climate changes. Since we are not very good at predicting future climate changes, the results of impact studies are inherently 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. The figure below was taken from the United States Centers for Disease Control (CDC). The figure seems to imply that rising CO2 will cause an increase in all of the health-related issues shown. We have already discussed the uncertainty associated with future predictions of the two items on the upper left of the figure, increases in severe weather and changes in extreme temperatures, which should include both heat and cold. It seems as if the CDC is attempting to shock or scare people with this array of possible consequences without at all addressing the uncertainty in the climate change senario they selected. Someone more cynical may say that this is an effort by the agency to expand and increase funding.

Figure showing the projected impacts to human health due to projected climate changes (Source CDC page on Climate and Health).

Another issue with impact studies is 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 humans and other life within will adapt. One would need to know both the magnitude of the climate changes as well as the rate of change as that would influence the ability of life to adapt. One would also have to understand how life in the ecosystem would respond to climate changes. In addition there will likely be unforeseen changes in human living conditions and environmental engineering with advancing technology that will influence our vulnerability to climate changes. These are not easy questions to answer with much certainty.

Below is a list of reasonable considerations for climate changes based on current knowledge. Keep in mind that climate change is expected even without human influences. There will always be ongoing concerns with the ability to supply all people worldwide with fresh water and food. Some claim that this will be made tougher due to climate changes stemming from greenhouse gases. However, we cannot just expect that these problems will go away if we just stop adding greenhouse gases. We need to address water and food issues regardless of any human-caused climate changes.

  1. Continued Sea level rise. This is certain as long as surface temperature increases, and may have been happening since the end of the last ice age, which means it may not be completely dependent on short-term fluctuations in surface temperature. This implies that it may not stop even if we stopped adding greenhouse gases to the atmosphere. Sea level rise is something that needs to be planned for as it is likely to continue. And if the worst climate model projections come true, sea level could rise as much as 1.5 meters (150 cm) more by 2100 (does not seem likely).
  2. Forests and other ecosystems must migrate or adapt to climate changes
  3. Agriculture. Changes in Temperature and precipitation patterns will shift growing zones.
  4. Human health. In the developed world, advances in technology and health care mean people are living longer and helthier than ever. This trend is likely to continue even with climate changes. There are still issues with making this technology available throughout the world, but those are not related to climate change.
  5. As surface warms, the hydrological cycle becomes more active. This may result in the following:

The link below is from the EPA's pages on the impacts of climate change. Again, this government website is biased toward possible negative impacts of climate changes resulting from human emissions of greenhouse gases and not straightfoward about the uncertainties in the connection between human emissons, climate changes, and the impacts of climate changes. Given our large uncertainties in the prediction of future climate, the effects of increased greenhouse gases on climate change, and the impacts that climate changes will have on ecosystems, the information presented by EPA leans toward a worse-case senario. In the web pages, the EPA cites scientific studies that fit their idealogy, while ignoring those that do not. The message put forth by the EPA is not a balanced scientific assessment of our current understanding of possible climate changes and the possible impacts of these changes. The information seems to be presented more as facts without regard to the uncertainty and conflicting scienfic studies.

Link to EPA Page on Future Climate Changes and Impacts

[Home] [Lectures] [Previous] [Next]