[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 conclusion of the IPCC report, which is based largely on climate model simulations, 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 briefly look at some of the observed changes in temperature and other climate variables. A more detailed look at measurements of changes in global average temperature is provided in upcoming lectures. 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's conclusion 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. Take a look at 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 partially correlated with each other cannot be used as proof that one caused the other, i.e., that greenhouse gas increases were the cause of the warming and subsequent reduction in arctic sea ice.

We now have the ability to document all kinds of climate changes over much of the Earth. If most of the recently observed climate change has resulted mainly because of greenhouse gas emissions, then some of the changes listed below might be considered as reasons to reduce emissions. 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.

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 was 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. Instructor's Note: Regardless of whether or not you believe the CDC should be spending money in this area, it looks funding was changed due to the influence of President Trump. I noticed that some of the web page links concerning climate change on both the CDC and EPA pages no longer work. Now that President Biden has taken over, it will be interesting to see if these pages come back.

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:

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