It’s the middle of winter here in the United States, and when there are inches of snow and ice on the ground, it’s easy to try and dismiss global warming. But just like a budding athlete can have great moments and poor ones, and on average be improving, global warming is all about averages. Different areas around the globe have different temperatures at different times of the year, but on average, global surface temperatures have been increasing. This increase is due to greenhouse gases: compounds that are good at absorbing and trapping heat in the atmosphere. Though a future video will look at the exact mechanism in detail, heat is absorbed by the molecules as infrared radiation, which causes them to vibrate back and forth. The biggest culprits that humans directly add to the atmosphere include carbon dioxide, methane, and nitrous oxide, the bulk of which are produced from burning fossil fuels for electricity and transportation. Specifically, carbon dioxide makes up the majority of greenhouse gases released by humans, with its atmospheric levels increasing each year.
However, the biggest player in the greenhouse effect, water vapor, is not produced in great quantities directly by human activity. But, an increase in global temperatures from the directly added greenhouse gasses, increases the atmosphere’s capacity to hold onto water vapor, thus indirectly increasing the levels of water vapor in the atmosphere. Greenhouse gas production by humans effectively creates a positive feedback loop, through this water vapor effect and others, to increase global temperatures. Much like many other systems in science, the earth can be thought of as a system in dynamic equilibrium. Specifically, carbon flows between oceans, plants and animals, and the atmosphere in a balanced way. And though the amount of carbon released into the atmosphere by burning fossil fuels is much smaller than the other sources, it disrupts the established equilibrium by mobilizing carbon from the previously inaccessible geological sources.
One measurement which supports that the rising CO2 in the atmosphere is from human activity, is the relative percentage of different isotopes of carbon. Carbon has two stable isotopes in carbon 12 and carbon 13. Compared to the current atmosphere, fossil fuels are particularly high in carbon 12. The increasing carbon dioxide in the atmosphere with the increasing percentage of carbon 12 suggests that fossil fuels are the major source of the carbon. We’ve looked at what’s occurring in our atmosphere, but could the sun have any role in global warming? Though the earth’s surface temperatures have been rising, solar irradiance has been relatively constant since the 1970s. Furthermore, if solar activity were to blame, we would expect both the troposphere and the stratosphere to be increasing in temperature. The observed warming in the troposphere and cooling in the stratosphere is instead consistent with a growing greenhouse effect. A recent review of climate papers estimated that up to 97% of climate scientists agree that global warming is occurring. That level of agreement for any scientific phenomenon is extraordinary.
If 97 out of 100 doctors told a patient that he needed a liver transplant, do you think he would listen? But the consensus for global warming is even stronger than a small group of individuals, as the best and brightest scientific communities both in the United States and abroad have all come to agree that global warming is occurring and must be addressed. Global warming will have a myriad of effects on our planet, hence why many scientists prefer the term “global climate change.” We expect more severe weather, including changing rainfall patterns leading to floods and droughts. Melting sea ice will decrease the salinity of our oceans and may disrupt the thermohaline circulation, which is responsible for bringing warmth to regions farther from the equator, including much of Europe. Increasing CO2 increases the acidity of our oceans which could have devastating effects on aquatic plants and animals.
These effects, along with the predicted ecological effects of global warming could even threaten our food security. Some robust studies have even suggested that climate change would stunt our future society and economy from living up to its full potential. Many techniques are being discussed to limit the effects of global warming, including carbon capture, changing agriculture practices, and ocean fertilization. Above all, moving toward renewable, emission-free sources of electricity and away from fossil fuels can eliminate our major source of carbon dioxide emissions. To make it easier for environmentalists, policymakers, and economists to mitigate the effects of global warming in a cost-effective manner, a goal of limiting global warming to 2 degrees in comparison to pre-industrial levels was adopted. Though the achievability of that goal has recently come into question, we know for certain that delaying action will further limit our ability to mitigate global warming and will require our future actions to be more drastic and expensive.