Climate Change and Implications

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. On this page we will examine the recent observed changes in temperture and climate as well as some of the impacts of those changes. We will then briefly discuss the IPCC 2007 report's estimation of what caused the recent observed changes. Finally, we will take a look at what could happen in the future if some of the predictions made by current climate models are correct.

Climate has changed during the past century. Below is a list of some of the changes that have occurred based on information contained in Climate Change 2007: The Physical Science Basis. Note that these changes are allegedly based largely on observations and to a lesser extent models, so we can place more confidence that these are correct in comparison to predictions of future climate change. However, some of the recent climate changes described in the latest IPCC Report are questioned by climate researchers. Please keep in mind that observed changes do not provide strong evidence for why the changes have happened. Arctic sea ice has decreased in coverage since 1980. We are quite certain of that. However, that observation does not prove that the reason for the decrease in Arctic sea ice is human emissions of greenhouse gases. 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 arctic sea ice has decreased, however the fact that these two events are correlated with each other cannot be used as proof that one caused the other.

• Global mean surface temperature has increased by about 0.75°C (1.4°F) since 1850
• 17 of the previous 18 years (1995-2012) rank among the 17 warmest years of the instrumental temperature record (since 1850). Instructor's note: Few people argue that global average surface temperature has not risen since 1850. There are questions about how much it has warmed. Uncertainty comes about because adjustments need to be made to measured thermometer records for things like changes in instrumentation, changes in the location of the thermometer with time, changes in population density near the thermometers, etc. Different reasearch groups use different adjustment methods. One also has to consider some of the issues recently brought to light in the climategate scandal, which questions the scientific integrity of some of those responsible for publishing trends in global temperatures. If you are interested in climategate, I suggest you do a web search and read several articles on both sides.
• Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m. Instructor's note: This statement has been widely questioned. Since 2003, we have direct measurements of ocean temperatures down to 700 meters using the Argo network of 3441 Ocean Buoys. This data is inconclusive as to the trend in ocean temperatures at various depths over the time period of its operation. The steady increase in ocean temperature predicted by many climate models has not been observed by the Argo instruments.
• Widespread changes in extreme temperture have been observed over the last 50 years. Cold days, cold nights, and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent (see Table SPM-2, IPCC 2007). Instructors note: I have some question about the ability to prove or disprove these conclusions given the limited spatial and temporal coverage of data as well as our limited understanding of the natural variation of these events.
• Global sea level has risen 0.12-0.22 meters (4.7-9.0 inches) since 1900.
• Widespread decreases in glaciers and icecaps (not including Greenland and Antarctica) have contributed to sea level rise
• The remaining sea level rise due to thermal expansion of oceans.
• Global precipitation patterns have changed
• General increase over eastern parts of North and South America and nothern Europe and Asia
• Slight decrease in many subtropical regions (20-35)°Latitude
• Increase in the frequency of heavy rain events over many land areas
• More intense and longer droughts now more likely in tropics and subtropics. Instructor's note: I again question that we have enough data over a long enough period of time to be able to prove or disprove these claims.
• Significant decrease in arctic sea ice, particularly in the spring and summer seasons. Instructor's note: We have been able to monitor arctic sea ice with satellites since 1979. Over this period there has been a significant decrease in Arctic sea ice coverage, with a record low sea ice area in 2012. Over the same period, though, there has been an increase in Antarctic sea ice coverage, with a record high sea ice area in 2012. Prior to the 1979 and the satellite record, there are accounts of low sea ice periods in the Arctic, e.g., a November 1922 article in Monthly Weather Review, a April 1923 article in the "London Daily News", a April 1939 article in the "Examiner", which talks of an ice-free North Kara Sea and a sea ice line north of 82° latitude. These articles suggest that there are natural cycles of sea ice changes in the Arctic. Today's sea ice extent is likely influenced by both natural variation and any temperature changes related to greenhouse has increases.
• Northern hemisphere snow cover has decreased by about 10%. Instructor's note: While Northern Hemisphere snow cover was relatively low in the decades of the 1980s and 1990s, it has certainly not been low for the 2001 - 2010 period ( article)
• No conclusive change in severe weather events (such as tornadoes and hurricanes). Some reasearch groups are claiming that hurricanes are becoming more intense, while other groups dispute this claim.
• Limited observational evidence shows that some biological systems have been affected by recent climate changes.
• Lengthening of middle and high latitude growing seasons
• Poleward and altitudinal shifts of plant and animal ranges
• Earlier flowering of trees, emergence of insects, and egg-laying in birds.

Attributing Observed Climate Changes to Human Activities

The most recent IPCC report (2007) is now more forceful in its statement concerning the anthropogenic influence on observed climate changes: "Most of the observed increase in globally averaged tempertures since the mid-20th century is very likely due to the observed increase in greenhouse gas concentrations." This is different from the previous statement "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations." 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. 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 Climate Change Impacts In The USA are Already (Not) Happening.

Climate is expected to continue to change in the future. The following list is based on climate model projected changes due to addition of greenhouse gases. Because this list is based on climate model projections, these changes are by no means certain to happen.

• Projected increase of global average surface temperature of 1.1-6.4°C by 2100.
• Projected sea level rise of 0.18 to 0.59 meters (7 - 23 inches) by 2100
• Likely increase in precipitation intensity. More heavy rain events and more severe droughts.
• Reduction in areal coverage of snow, glaciers, and sea ice.
• Disruptive changes in biological systems

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:

• Human health, natural ecological systems, and socioeconomic systems are all sensitive to both the magnitude and the rate of climate change
• Many physical and ecological systems will be simultaneously affected
• The ability of natural ecological systems to migrate appears to be much slower than the predicted rate of climate change estimated by climate models
• Climate change can add to existing environmental stresses, some of which are brought on by other human activities, such as deforesting a region for human settlement

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.

Health Impacts	Water Resources Impacts	Forest Impacts
Coastal Areas	Species and Natural Areas	Agriculture Impacts