Course: BIS 105 Environmental Biology

Unit 13 Learning Module

Climate Projections

In the previous section we discovered that the global warming of approximately 1°C over the past 200 years was human induced through an enhancement of the natural greenhouse effect. We learned that the burning of fossil fuels has upset the natural carbon cycle, which has steadily increased the amount of carbon dioxide (CO_2) in the atmosphere since the 1750s. Finally we looked at ancillary evidence of this warming to see the immediate impact of these changes. In this module we will investigate the findings of the Intergovernmental Panel on Climate Change (IPCC) and look at future climate projections. We will inspect these findings and analyze their impacts on a global scale.

Who is Responsible? Factors to Consider

In 2007, the IPCC was awarded a share of the Nobel Prize for its work in the area of global climate change. The IPCC is organized through the United Nations and is composed of over 3,000 scientists from around the world who are working together to understand current climate change and project future climate scenarios. As of 2013, the IPCC has released four comprehensive reports, and it has concluded, “Most of the observed increase in global average temperature since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” This widely known statement essentially means that the probability of occurrence is greater than 90% that the current global warming is caused by humans burning fossil fuels. In response to these findings, the United Nations Framework Convention on Climate Change has called for numerous international meetings in cities including Kyoto, Bali, Copenhagen, and others where the leaders of world have gathered to discuss strategies to mitigate this looming disaster. At these meetings, scientists, politicians and world leaders review the current state of knowledge about the problem and strategize for the future. This section will take a large-scale view of the global challenges of climate change.

Over the past few years, China has surpassed the United States to become the nation that emits more greenhouse gasses than any other. Currently, China is responsible for just over 25% of global CO_2 emissions, which are approximately 30 Gt per year, with the United States in a close second place. It is important to consider population when reviewing these numbers because there are over four times as many people living in China than in the United States. When you compare these two countries on a per capita basis, the average U.S. citizen emits approximately 19 metric tons of CO_2 per year while the average Chinese citizen emits approximately 5 metric tons. In 2009, the United States consumed more than double the amount oil than the second largest consumer, China, according to the U.S. Energy Information Administration. Topping the list in per capita CO_2 emissions is the oil rich nation of Qatar. This small country located on the Persian Gulf has the largest per capita production of oil and natural gas. It also has the world’s highest gross domestic product (GDP) per capita. An average citizen in this country emits nearly 60 metric tons of CO_2 into the atmosphere each year.

Rather than point the finger at individual countries, let’s examine the bigger problem. The maps below distort the size of each country based on a certain variable, like CO_2 emissions, with respect to the rest of the world. In the upper left panel, the map is based on population, which is why China and India appear so large. The upper right map distorts the size of the country based upon fuel use. Notice that the United States, much of Europe, and Japan are expanded the most, while Africa, the Middle East, and much of South America are barely visible. Compare these two maps with absolute wealth and carbon emissions and the story is quite clear. The industrialized and wealthy nations are responsible for the largest quantities of carbon emissions and fuel imports. These societies are built on the foundation of energy production through the consumption of fossil fuels.

The bottom two panels tell another aspect of this story. Focus first on the graph in the lower right, which shows forest loss by country. The world’s forest biomes are a large part of the CO_2 cycle and with deforestation, a large sink for atmospheric CO_2 is taken away. Notice that deforestation is most prevalent in Africa, South America, and Indonesia while the United States is barely visible on this map. In the United States, reforestation is practiced, but in the rainforests of the world, which are those areas in South America, Africa, and Indonesia that are ballooned on this map, deforestation is commonplace.

The last graph in the figure distorts each country’s size according to poverty. Much of Asia and Africa are distorted the most, and it is in these regions that we need to pay close attention over the upcoming years. Many of the nations found within these countries are what economists and politicians call “emerging economies.” Although much of the current abundance of CO_2 in the atmosphere is from developed countries such as the United States, CO_2 emissions from these countries are not increasing with time according to a report from the Energy Information Administration. In the figure below, the world’s CO_2 emissions from coal combustion in millions of metric tons are plotted against time. Notice that countries of the Organization for Economic Co-operation and Development (OECD), which comprises a large group of developed and industrialized nations, have not increased their CO_2 emissions from coal combustion since 1990, and future projections also reveal a flat line in CO_2 emissions. Compare this to the non-OECD countries, many of which are emerging economies like China and India, and you see that CO_2 emissions are set to triple in the next 25 years. There is much debate over information like this now that recent climate change has been linked so closely to anthropogenic emission of CO_2. This debate revolves around the fact that developed nations used coal, oil, and natural gas during a time when the impacts of CO_2 and climate change were not well researched. This meant that during the time these countries, including the United States, industrialized there were no regulations on the emissions of CO_2. Now that CO_2 emissions have been shown to cause global warming, pressure is being applied to these emerging economies to regulate and control their CO_2 emissions. This is subject of much of the debate at the international climate summits at Kyoto, Bali, and Copenhagen. What is important to remember when discussing developed countries vs. emerging economies is that the per capita emissions of CO_2 in emerging economies are approximately one third of those for developed countries.

Climate Projections

One of the greatest obstacles climate scientists face in educating the public on issues of climate change is time. Most people take weather and climate to be one branch of scientific study. In reality, this could not be further from the truth. Weather and climate are two separate fields of study that are joined only by one definition—climate is the average of weather. It is important to understand this statement because people—news reporters, broadcast meteorologists, politicians, and even scientists—often make the mistake of attributing weather events, such as Hurricane Katrina (2005), to global climate change. Katrina was a weather event and, as such, it cannot be said to have been caused by global climate change. Are the ingredients for stronger hurricanes present in greater frequency now than they have been in the past? That’s the type of question climate scientists seek to answer, and they do so by analyzing decades worth of data. Thirty years is the lowest value used in the denominator of climate calculations. In other words, 30 years is the shortest time period over which weather can be averaged to extract climate information. Therefore, it is impossible to blame a single weather event on climate change—this branch of science does not work that way.

To better understand the differences between weather and climate, take a look at the figure below which shows in red the actual high temperatures for each day in 2005 in Champaign, Illinois, compared to the average high temperature in black over a period beginning in 1899 and ending in 2009. It is completely normal for the temperature to vary ±20°F around this average. In 2005 there were only a handful of days where the actual high was the same as the average high. This graph shows the highly variable and chaotic behavior of weather. But, when data from a long span of time is averaged, the climatological mean emerges.

To think of it another way, imagine you are in a large lecture hall with over 300 college students. If the professor were to call out one student and try to predict the course of her life over the next 70 years it would be nearly impossible! It would even be difficult to predict when that person would eat her next meal. However, the professor could project with great confidence that on average, most of the people in the room will eat dinner at 6:30PM on a given night. Beyond this meal, most of them will graduate from college by the time they are 23 years old. Many will be married by 27 years old and have their first children at 30. Most will have a job by the time they are 24 and most will have a job they like by 34. Most will have a total of 2.1 children by the time they are 36, and by the time they are 50 most will have gone to the doctor to have their first routine procedure. Most will retire at 67, and since they are college grads in the United States, there is a safe bet that they will retire with over a million dollars in assets. On average, the men in the room will die at 85 years old and most of the women will die before their ninetieth birthday. Now, if the professor were to single out one individual, the chances that her life would follow this path exactly are small, but when an entire class of 300 is averaged, this is the result. Weather is like the individual life. Climate is like the average of 300 lives. Weather and climate are two separate branches of study in atmospheric science.

In addition to keeping in mind the difference between weather and climate, remember that the focus of this unit is global climate change. It is tempting to forget the global nature of this problem because it is happening very slowly on a large scale and it is averaged over long time periods. Recall the differences between weather and climate and remember that in conjunction with global warming there can still be weather events that take temperatures far below normal. The temptation during these events is to discount the science behind global climate change. For example, during the winter of 2009-2010, the weather patterns were such that the east coast of the United States experienced repeated record-setting snowstorms and cold air outbreaks. Many television news reports, weather broadcasts, and newspaper headlines scoffed at the idea of global warming during this winter and proclaimed that it was not happening or that it was a hoax. The shortsightedness of such responses is evidenced by the fact that globally, 2009 and 2010 were among the warmest years during the instrument record: 2009 ranked seventh, and 2010 tied for first. These were likely two of the warmest years of the last 1,300.

Climate Modeling and Future Climate Predictions

Sometimes people discount climate predictions based on their understanding of weather predictions. They will say something like, “Meteorologists can’t even give me a reliable forecast of the weather over the next three days, how am I supposed to trust them to give me the forecast for the next 100 years.” You’re not! Climate scientists do not use weather forecast models to forecast climate conditions 100 years in advance. The computer models that are used to predict the weather over the next few days are entirely different from those used to predict the climate. Instead of predicting the highly chaotic nature of temperature, precipitation, and other common weather variables at very high spatial and temporal resolution, climate models forecast changes in the flux of energy between earth and its atmosphere and space. These two computer-modeling techniques differ substantially in their computational expense as well. Although weather forecast models are run on extremely fast computer systems at the National Center for Environmental Prediction, the fastest computers in the world, like the Earth Simulator in Japan and Blue Waters at the University of Illinois at Urbana-Champaign are charged with climate simulations.

The petascale computing facility “Blue Waters” located at the University of Illinois at Urbana-Champaign.

What are these climate models predicting will happen by the year 2100? First, we will look at the global average surface temperature projections. The figure below plots global surface warming against time with the present day in the middle of this chart. Recall that over the last 200 years, there has been a 1°C increase in global temperatures, and that the rate of change has been extremely fast compared to natural changes in the earth’s climate. The graphs show the range of model projections from different climate simulation scenarios based upon various greenhouse gas emission scenarios (left graph). Focus on the top and bottom curves in the right panel, which show the most dramatic warming and the most conservative warming. The worst-case scenario, found in the top line, shows the “business as usual” projections. If nothing is done to mitigate the emission of greenhouse gases into the atmosphere, these climate models are predicting a 4°C to 6°C increase in global average temperature by 2100. The best-case scenario, from a climate change perspective, would be for a cessation of CO_2 emissions or for the current emission rates to not increase. In this case, there would still be a warming of 0.5° to 2°C by 2100 as indicated by the bottom curves.

Left – multiple climate model projections (or scenarios) of greenhouse gas emissions (including CO2, CH4 and N2O) emissions in Gt-CO2-equivalent through 2100. Right – multiple climate model projections of globally averaged surface air temperature through 2100.

In addition to predicting warming of the atmosphere, climate models also suggest that sea level will continue to rise. Since 1880, sea level has risen 20 cm (approximately 8 inches) as seen below. This rise has been primarily the result of the water thermally expanding as it warms along with the atmosphere. Polar ice cap melt from land-based ice sheets and glaciers has also added to increase in sea level. Recent projections by the US National Research Council indicate sea level will rise over the 21st century between 56 and 200 cm (22 and 79 in).

Measured sea level rise since 1880. The different colors represent different data sets used to make this graph.

How much confidence can we place in predictions about temperature and sea level by climate scientists? Let’s take a little detour before we address this important question directly. Imagine you are contemplating signing up with a psychic so you can better plan for the future—why save for retirement if money is tight and you’re not sure how long you’ll live? But you are uncertain about whether she can really see what lies ahead. You could pay her $20 a week for her predictions, and discover over time whether they come true or not. The trouble is, during this trial period you wouldn’t know whether to spend your money as fast as you make it or put some aside. But you come up with a better plan. You’ll pay the psychic $20 one time, but instead of asking her to predict your future, you’ll ask her to tell what has happened to you in the past week. If she gets that right, she gets your business.

Along similar lines, climate scientists assess the trustworthiness of their models by checking how well they “predict” the past. In the figure below, 58 different climate model simulations were tasked with predicting the past climate from 1900 to 2005. By comparing the model simulations to the observed temperature record the scientists with the IPCC tested the accuracy of their models. The yellow lines in the top panel trace out the individual model simulations, the red line shows the model ensemble mean, and the black line represents the actual observed mean temperature. The models performed exceedingly well, as evidenced by the very small variability around the observed temperature. The success of this test demonstrates the high-quality construction of these models and shows they are capable of accurately projecting the earth’s future climate.

Top panel - Climate model simulations of the global mean surface temperature compared to the observed global mean surface temperature in black. Each yellow line is one of 58 climate model simulations of which the red line is the ensemble mean. Bottom panel – 19 climate model simulations in blue with the ensemble mean in dark blue. These simulations were run without anthropogenic influences. The thick black line is the observed global mean surface temperature. For a description of each scenario, please click here

Together, model simulations and the figure below of global surface temperature comparisons present a compelling argument that current climate change is caused in large part by humans. The bottom panel of the model simulation figure shows 19 climate model simulations between 1900 and 2000 with human influences left out of the simulations. The thick black line represents the observed global mean surface temperature over this time. Compare this figure with the below figure of global surface temperature comparisons, which depicts a series of graphs that plot temperature anomalies against time from the early 1900s to 2000. The blue color shading on these graphs shows the computer model projections without anthropogenic effects, while the pink shading includes them. The black line represents the actual measured air temperatures in each of the locations over which the inlaid graphs are positioned. Notice that without humans the blue shading stays level or decreases with time. Compared with the pink shading and the black line, which both increase with time, and we find that these climate simulations cannot accurately represent the past climate without anthropogenic effects. Simply put, these models are unable to represent our current climate without greenhouse contributions from humans. Rigorous testing like this proves these models are robust and well-designed to simulate future climate conditions.

Global Surface Temperature Comparisons - Comparison of regional and global scale surface temperature 1900-2000. Pink shading indicates the model predicted surface temperature using only natural forcings. The blue indicates model predicted surface temperature using natural and anthropogenic forcings. The black lines represent the actual observations.

The IPCC began its work in the early 1990s and they have released four reports on climate and climate change. In each report they have included evidence as shown in the sections above. Since a few decades have passed since their initial reports, we can compare the actual changes since 1990 to the IPCC forecasts. The below figure, Observed Temperatures vs. Projected Temperatures, compares the observed global average surface temperature to each of the first three reports (the fourth was released in 2007). This figure reveals that both the second (SAR) and third (TAR) reports have been conservative in the projection of globally averaged temperature. It also shows that the observed warming has fallen into the range of expected warming by the IPCC. Due to their success in accurately predicting changes in earth’s climate over this time period, the entire body of scientists shared a part of the 2007 Nobel Prize.

Observed Temperatures vs. Projected Temperatures - Observed global average surface temperatures (black line) overlaid on the temperature projections of the first IPCC report (FAR), second report (SAR) and third report (TAR).

Global Impacts of Climate Change

Globally, an increase of between 2°C and 6°C in mean surface temperature is expected by the year 2100. Regionally, these values may differ substantially, and some locations may actually cool over the next century. The hardest hit locations will be the in the high northerly latitudes of the Arctic. The below figure depicts the variation in expected increases in surface air temperature for the time periods of 2011-2030, 2046-2065, and 2080-2099 with color shading for three different models (B1, A1B, and A2). Notice that in all of these images, the greatest changes are expected to occur at high northerly latitudes. If these projections hold true, ice and snow cover will continue to retreat and enhance the ice-albedo effect discussed earlier.

Aside from air temperature, global precipitation patterns and amounts are expected to change. As the atmosphere warms, its ability to hold water vapor increases, which leads to more evaporation from water on the earth’s surface. As this water condenses in the earth’s atmosphere to form clouds and precipitation, the distribution of the precipitation will vary greatly. Current projections forecast an increase in precipitation in the tropics and polar latitudes, with drier conditions over the mid-latitudes. Even though there will be more water vapor in the atmosphere, the distribution of precipitation may be such that large regions formerly unused to drought may be subjected to prolonged dry periods. Although more areas are expected to experience prolonged drought, these projections suggest that when it does rain, rainfall will arrive in much greater amounts over shorter time periods. This will lead to increased flash flooding, the deadliest weather phenomenon in the United States.

Changes in Precipitation - Average change in precipitation December to February (left), and average change in precipitation June to August (right).

The goal of climate science is not to craft public policy on global warming. It is to provide the public and policymakers alike with reasonable projections about future climate conditions. This information should be used to show the potential impacts of our presence on the climate system so as to form the best possible mitigation plans. Current projections show that if we are able to slow greenhouse gas emissions, the climate system will respond with the least amount of warming. They also suggest that if we continue with "business as usual" the change in the global climate will be great in magnitude and occur very quickly—both beyond past "natural" change.