Understanding something as complicated as climate change is really tough. So it’s easy to understand why people don’t always get things right. But it’s much easier to explain why the term “global warming” is misleading than it is to explain why some climate-change messages are only partially understood. So I put the “partial misconceptions” in a separate blog.

Partial Misconception: The greenhouse warming is due to carbon dioxide. Figure 4 shows that slightly over half of the warming near Earth’s surface is caused by carbon dioxide (CO2), with other gases – methane (CH4), Nitric oxide (N2O), halocarbons, and ozone in the lower atmosphere, accounting for the rest of the “forcing.” What is forcing? Forcing can be thought of as a “push” that warms (or cools) the Earth system.

The warming that results is actually larger then you might expect from an increase in these gases alone. This is because the warming surface and air leads to more water vapor, which is also a greenhouse gas. This leads us to the next partial misconception.

Figure 4. Effect of greenhouse gases and aerosols on surface air temperature warming, in terms of “forcings.” From 2007 report, Intergovernmental Panel on Climate Change.

Misconception: Carbon dioxide is the most important greenhouse gas. Certainly this is what you might expect from a first glance of Figure 4. But where is water vapor? I was taught as an Atmospheric Science graduate student that water vapor was the primary greenhouse gas, but carbon dioxide was also important. Modeling studies with various degrees of simplification confirm this first impression. A nice summary can be found on the RealClimate blog.

Why, then, do so many people say that carbon dioxide is the “most important greenhouse gas.” It’s probably because of figures like Figure 4. Note a very important adjective at the bottom which is often ignored, “anthropogenic,” meaning “made by humans.” Humans of course affect water vapor as well, but it cycles through very fast, and the amount of water vapor in the air is basically controlled by the temperature of the air and surface. In a climate model, water vapor continuously adjusts to the conditions within the model, while anthropogenic greenhouse gases in Figure 4 are adjusted by those who run the model.

Put another way, water vapor doesn’t appear in the “forcing” terms for climate models, because it is “internal” to the system. It changes as the result of a “feedback” within the model. Thus external inputs like solar radiation, changes in ground cover, and gases introduced into the atmosphere by human activity are counted as “forcing” but water vapor as not.

In short, we can say that carbon dioxide is the most important greenhouse gas whose amount people are directly altering. Not just in models, but in real life.

Partial Misconception: The warming climate means more exposure to dangerous diseases. I say “partial misconception” because there are multiple factors that change our exposure to disease. Many articles in scientific journals and newspapers discuss increased exposure to malaria, for example, in a warming climate. But that is not the whole story. For example, in the United States, malaria was a real threat over much of the country in the 1700s and the 1800s, and even into the early 20th century. However, public health efforts such as mosquito control and changes in peoples’ habits (for example, using window screens to keep out mosquitoes or staying indoors from dusk to dawn) have largely removed the malaria threat. Similarly, world travel spreads germs, such as the West Nile virus, around the world. This is not a new phenomenon. Europeans coming to the Americas brought small pox with them, leading to the tragic death of countless Native Americans. And populations moving into new areas can expose themselves to new germs.

However, we cannot ignore the fact that vectors for existing diseases will migrate with their preferred climate. Thus at some time in the future, some diseases will show up in areas where they haven’t been before; and in other areas where they have been suppressed.

Partial misconception: The warming climate means more birds will die. Again, there are many factors involved. There are stories of bird populations suffering because food supplies (for example caterpillars) are no longer available when the birds need them, because the two species are responding differently to climate change. However, songbird populations have also suffered because the scarcity of predators like wolves has led to an increase in the number of animals (like raccoons) who eat birds’ eggs. Similarly, pesticides have done serious harm to bird populations. This contributed to a ban on the use of the insecticide DDT in many countries. Finally, the West Nile virus has led to the deaths of many birds (although the magpies and crows, which fell victim to West Nile, seem to be recovering here in Boulder).

Once again, we cannot ignore the impact of climate change. If climate changes continue at the predicted rates, then the entire ecosystem will have to adjust to a new seasonal cycle. This will not be a smooth process: different plants and animals will respond in different ways. And, as in the case of the birds and caterpillars, the food supply will be interrupted at critical times.

Partial Misconception: If we cut back on our production of greenhouse gases, global warming will “go away.” This is true only over a very long period of time. It will take hundreds of years to decrease the carbon dioxide content back to pre-industrial levels through natural processes (the lifetime of carbon dioxide in the atmosphere is around 120 years). This does not mean we shouldn’t consider reducing carbon-dioxide emissions, because continuing the increase in carbon dioxide leads to even more warming than if we slow down the increase in carbon dioxide. One hopeful note is that not all greenhouse gases last as long as carbon dioxide, so reducing their release in the atmosphere might help on shorter time scales. Another hopeful note is that people are studying ways to take carbon dioxide out of the atmosphere, but this is the subject of another blog.

So, when you read or hear about the effects of people on the environment, or try to figure out what you can do to help the environment, please remember that we affect our environments in many ways. Similarly, actions we take to help our environment can improve our environment in many ways. But responding to climate change will remain a challenge for years to come.

As noted in previous blogs, many of us don’t understand the terms people use in describing climate change; nor do we always understand how ideas related to global climate change relate to everyday life. So I decided it would be useful to write about some of these common misconceptions or partial misconceptions. I’ll start with the misconceptions.

Misconception: The term “global warming” means the temperature is getting warmer everywhere. “Global warming” sounds to many (including me) like the temperature should be warming everywhere. If there is “global warming” shouldn’t it be getting warmer where I live? Or, if it’s not getting warmer where I live, how can “global warming” be happening!

If you look at the recent temperature records from several GLOBE schools, the temperature does seem to be warming gradually in some places. But other schools show a cooling trend. It is the same way with the stations used to monitor climate change. As noted in my July 2008 blog, the global average temperature change is often much less than the trends at local sites.

The term “global warming” really means that the yearly average of the temperature averaged over all the Earth’s surface is rising over time scales of several years.

Misconception: We just had a month that was the coldest on record. That means that the climate has started to cool again. When I stop thinking like a scientist, I also briefly think – or hope – that a cold month means that “global warming” will go away. But a record cold day or month doesn’t mean that the climate is getting cooler on the long term.

In a warming climate, there are still changes in both directions from day to day, month to month, and year to year. But there will be fewer record cold months. And there will be more periods of record high temperatures. For example, the city of Chicago in the Midwestern United States is having more heat waves, as illustrated by Figure 1 (taken from the blog, “Regional Climate Change, Part I: Iowa Dew Points and Chicago Heat Waves,” 22 March 2007).

Figure 1. Temperatures during Chicago, Illinois, USA heat waves. While the graph was made to show how the dew point has risen during the heat waves, the increase of the number of points (heat waves) with time shows that there are more heat waves than there used to be. Figure based on data from Changnon et al. (Climate Research, 2003).

Misconception: Earth’s temperature will steadily warm (as in “This year is warmer than last year, and next year will be warmer than this year.”). The globally-averaged yearly temperature record in Figure 2 has many dips and peaks. It is well-known that strong El Nino events, through spreading warm water across the tropical Pacific, will cause peaks in the record (There were strong El Ninos for example in 1982-3 and 1997-8). Similarly, volcanic eruptions can cool the surface temperatures globally for a year or two.

Figure 2. Annual average temperatures, averaged over the Earth. Data from the UK Hadley Centre.

There will be even more extreme year-to-year changes locally. Some regions will have colder-than-normal periods due to persistent airflow from the Polar Regions. At the same time, there will have to be compensating airflow toward the poles in other regions, which will have warmer-than-normal periods. If you look at any local temperature record, such is the one in Figure 3; there are year-to-year changes that are faster than the overall warming trend. Even though there is a general upward trend in temperature as indicated by the straight line, the warmest year on record was 2000. On the other hand, 1998 was the warmest year in Figure 2.

Figure 3. Average annual temperature at the GLOBE School 4. Zakladi Skola in Jicin, Czech Republic. From 15 July 2008 blog.

Misconception: The “warming” scientists write about is not real. Many thermometers are showing warmer temperatures because their surroundings have changed over time, and this affects the global average You can find web sites showing weather stations next to buildings, air-conditioning heat exhausts, and so on. So this is certainly true for some sites. However, climate scientists try very hard to eliminate such sites from the climate record. There are literally thousands of weather stations in the United States today, and a similar density of sites exist in other parts of the developed world. These are used for many things, such as weather forecasting, keeping track of weather at airports or along roads or railroad tracks, or for education and outreach purposes by television stations or schools. But only a small fraction of these are used to document the global change in temperature. It is important to know that the temperature at any station is not taken at face value. Each measurement is checked carefully. For example, each station is compared to nearby stations to see if their temperatures are biased or just plain wrong.

At the GLOBE Learning Expedition, we saw a climate-monitoring station, on a rocky hill at the southern tip of Africa, away from any urban influence (11 August 2008 blog). And, only 30 per cent of the Earth’s surface is covered by land – the other 70% of the area is over the ocean. There, ships, buoys, and now satellites supply the needed measurements.

This does not mean that the warming recorded by sites that were once rural but are now surrounded by cities is not telling us something. Cities are warmer than the surrounding rural areas. They have more concrete and asphalt, which means that more of the incoming solar radiation is converted to heat rather than used in photosynthesis or evaporation. Also, factories, buildings, cars, and even people release energy that warms the environment. If you move from a rural area to a city, you will experience a warmer climate. However, this “urban heat island” has only a small effect on the global average because cities cover only a small fraction of Earth’s surface (See “Land Use: How Important for Climate, 11 June 2008).

Also, we need to remember that the famous surface-temperature curve shown in Figure 2 is not the only evidence that the climate is getting warmer. Satellite data also indicate warming at and near Earth’s surface, as does the shrinking of most glaciers and the smaller extent and thickness of Arctic sea ice (see, e.g., http://svs.gsfc.nasa.gov/goto?3464) . Furthermore, sea level is rising slowly, a result of more water in the ocean basins (from the melting of ice on land) and expansion (as the water gets warmer). And there is more water vapor in the atmosphere than there used to be, consistent with more evaporation (to be expected from water land and sea surface temperatures as well as warmer air).