Before we dive head-first into our exploration of the consequences of climate change I feel it would be worthwhile to refresh our understanding of the basic science behind global warming, climate change, and the difference between the two.
Global warming is caused by an energy imbalance between the solar radiation (i.e. sunlight energy) that hits the Earth and the heat (thermal energy) the Earth radiates back into space. The laws of physics dictate that the thermal energy emitted from the Earth and solar energy that strikes the Earth must be in equilibrium i.e. the energy the Earth receives has to equal the energy the Earth radiates.
Greenhouse gases emitted by humans, however, trap some of the thermal energy the Earth would normally emit into space causing an imbalance. In order to return to equilibrium, the planet must emit additional thermal energy thus raising the Earth’s temperature. How do these greenhouse gases trap heat?
By absorbing the infrared radiation emitted by the Earth’s surface (infrared radiation is analogous to heat).
A molecule’s chemical composition determines how it will interact with different wavelengths of light (i.e. types of radiation); so greenhouse gases, like methane & carbon dioxide, are simply molecules in the atmosphere that allow visible light emitted from the Sun to pass through but prevent infrared light radiating from the Earth’s surface to escape into outer space.
We understand the physics behind this process very well, in fact back in the 19th century the renowned Swedish chemist Svante Arrhenius calculated that a doubling of CO2 would cause a 4 degrees C rise in average global temperatures (above pre-industrial levels); today in 2017, the world’s best scientists calculate that a doubling of CO2 will cause a 1.5 to 4.5 degrees C rise in temperatures. (that’s impressive accuracy for a 100+ year old calculation!) So the science behind the greenhouse effect is well established.
We also know that fluctuations in the Earth’s temperature caused by the greenhouse effect can have a profound effect on the planet’s many ecosystems. This is climate change. By analyzing ice cores, tree rings, and other geological data climate scientists can determine how the Earth’s climate changes with corresponding increases in CO2 concentration. For example, the last time CO2 concentrations were above 400 ppm like they are today, global average temperatures were 3-4 degrees C higher than during the pre-industrial era and sea levels ranged between five to 40 meters higher than they are today. (Scripps Institute of Oceanography)
The terms climate change & global warming are often used interchangeably and I believe this leads to confusion and, in some cases, skepticism. When critics point to uncertainty in climate models as proof that global warming isn’t occurring they are fundamentally misunderstanding the science.
As we previously described, the increased greenhouse effect caused by human activity mandates global warming and this fact is grounded in centuries-old science. The connection between changes in CO2 concentration and changes in the climate is also a well-established fact, being bolstered by the geological evidence and historical data. The uncertainty in our climate models stems from our lack of data on climate sensitivity i.e. we’re not sure how sensitive today’s climate is to increases in CO2 and greenhouse gas concentrations caused by human activity. Changes in the composition of the Earth’s atmosphere typically have taken place over timespans of many millennia. However, humans have pumped billions of tonnes of carbon into the atmosphere in a span of time shorter than two centuries; carbon which had been locked away safely underground for well over 200 million years.
We just simply haven’t seen CO2 concentrations increase this rapidly before. That means we don’t have any historical examples that can tell us how quickly we should expect the climate system to respond to these changes. This is why our climate model projections contain so much uncertainty in regards to future risks. Will the effects of anthropogenic global warming fully manifest themselves over many centuries or much sooner than that? Will the changes occur gradually or will we experience abrupt shifts in the climate system? Is 2 degrees C of warming unmanageable or can we deal with a 3 degrees C increase? Or will disastrous consequences kick in well before we reach 2 degrees C of warming as we cross unforeseen climate tipping points?
Additionally, the climate system is infamously complex and we simply don’t have the computing power necessary to analyze the thousands of possible future scenarios (unless we crack quantum computing of course). Analytical modelers try to compensate for our lack of computing power by using a myriad of mathematical and statistical shortcuts to simplify the data, but these techniques can only get us so far.
However, all that being said, when our models are run in reverse they do accurately describe the historical changes in the climate we have already observed, demonstrating that the methodology behind our modeling is essentially correct. So it would be foolish to totally dismiss the predictions they make for our future. Also given the potentially catastrophic consequences of inaction and the limited time we have to act, we simply can’t wait a decade or two for models with near perfect precision. As I laid out in my previous post every ton of carbon we emit today is a ton carbon we can’t emit tomorrow, so the longer we wait the harder the problem is to solve until we eventually hit the point of no return.
Hopefully, you found this refresher to be useful. The next article in this series will examine how global warming has affected the climate at the poles, as well as expound upon the potential consequences of these changes.
