Four Graphics (And A Book) That Help Explain Climate Change

Though blizzards and cold snaps may have made you forget the news from last week, 2015 was the warmest year in NASA’s global temperature record, which dates back to 1880. During a January 2016 press conference (see the slides here), Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, explained that 2015 was 0.87 degrees C (1.57°F) above the 1951-80 average in the GISS surface temperature analysis (GISTEMP), one of four widely-cited global temperature analyses.

The statistical record is notable, but keep in mind that this year is just part of a much longer story about the climate. If you want to learn more about climate science as a whole rather than just the latest headlines, here are a few resources that you may find informative. The list is not comprehensive (and we are open to more suggestions), but it is a useful starting point for understanding climate science.

The plot above comes from an interactive graphic called “What’s Really Warming the World?” Put together by Eric Roston and Blacki Migliozzi of Bloomberg News (with assistance from NASA climatologists Gavin Schmidt and Kate Marvel), the chart does an excellent job of breaking down the various factors (greenhouse gases, aerosols, solar activity, orbital variations, etc.) that affect climate. It parses out visually how much each factor contributes. The bottom line: greenhouse gases are absolutely central to explaining global temperature trends since 1880. The screenshot above hints at what the interactive looks like, but I highly recommend heading over to Bloomberg to see the full graphic.

Another invaluable graphic for understanding climate change is the “radiative forcing bar chart” below. (You can read an interesting post by Schmidt that explains how these charts have evolved over the decades). At first glance, the chart from the fifth assessment report by the United Nations’ Intergovernmental Panel on Climate Change may seem technical and difficult to understand. It is. But it is well worth looking up the technical terms.

In short, you are looking at a balance sheet of the major types of emissions that have either a warming or cooling effect on climate. Bars that extend to the left of the 0 signify a cooling effect; bars that extend to the right signify warming. The longer the bar, the more warming or cooling a given type of emissions contributes. What becomes immediately obvious is that carbon dioxide (CO₂) and methane (CH₄) have the biggest warming influence by far. The other well-mixed greenhouse gases — halocarbons, nitrous oxide (N₂0), chlorofluorocarbons (CFCs), and hydrochlorofluorocarbons (HCFCs) play a much smaller role.

The situation gets messy when you look at the role that short-lived gases and aerosolsplay. Some gases like carbon monoxide (CO) and the non-methane volatile organic compounds (NMVOC) — such as benzene, ethanol, formaldehyde — contribute to warming, but not much. Others like NO_xactually slightly cool the climate overall if you consider how these gases interact with other substances in the atmosphere. Things get even messier if you look at aerosols. Mineral dust, sulfate, nitrate, and organic carbon have a cooling effect. On the other hand, black carbon causes warming. Albedochanges due to land use and changes in solar irradiance are minor in comparison to the other factors.

That’s a lot of variables, but one reason I like this chart is the error bars and the “level of confidence” column. The error bars give you a sense of how much uncertainty there is when it comes to the effects of various emissions. Look at the aerosol section, for instance, and you will see that the error bars are quite large and there is still some uncertainty about how aerosols affect clouds. The level of confidence column offers further clues to what scientists understand well and which areas they are less confident about. VH stands for very high confidence; H stands for high confidence; M stands for medium confidence; and L stands for low confidence.

What is striking is that even when you account for the error bars, there is little doubt that carbon dioxide and methane are warming the climate.