We’ve all heard of “climate change,” a term that feels so charged, but what does it really mean, and what is actually happening? Let’s break down the scientific definitions to help us really understand what researchers and climate professionals are talking about when they say “climate change.”
Scientifically, the term “climate change” describes long-term changes in the average weather, which we might experience as changes in temperature, precipitation, and other variables. Climate change can result from natural variations, but it can also be caused by human activity.
Read more in the blog Climate expert breaks down the basics of climate change by Dr. Justin Schoof, Director of the School of Earth Systems and Sustainability at Southern Illinois University.
Key terms about our planet's climate
Baseline emissions: Emissions of greenhouse gases that are not changed by human intervention
Cap: Mandated restraint as an upper limit on emissions. It is often used in reference to a cap on greenhouse gas emissions.
Carbon credit: Carbon credit is used in emission trading, where one credit gives the owner the right to emit one ton of CO2.
Carbon dioxide equivalent: A measure used to compare the emissions from various greenhouse gases based upon their global warming potential (GWP) compared to carbon dioxide.
Carbon footprint: The total amount of greenhouse gas emissions caused by an organization, event or production process.
Carbon neutral: Where an individual or company's carbon emissions are effectively reduced to zero through a combination of processes.
Carbon sequestration: The storage of carbon to prevent it from being in the atmosphere as carbon dioxide.
Carbon offset: An investment in a project that will lead to the prevention or removal of carbon dioxide from the atmosphere
Climate: The long-term average of daily weather.
Climate lag: The delay that occurs in climate change as a result of some factor that changes very slowly.
Greenhouse effect: When certain wavelengths of energy (heat) that is escaping from earth to space is slowed in escape by the absorption and re-emission of this energy by greenhouse gases.
Negative feedback mechanism: An outcome in nature that reduces a change in climate.
Net Zero: The balance between the amount of greenhouse gas produced and the amount removed from the atmosphere. Net zero occurs when the amount of greenhouse gases added are no more than the amount taken away.
Paleoclimatology: Study of ancient climates.
Positive feedback process: An outcome in nature that reinforces a change in climate
Radiation: Waves of energy that are produced by all objects.
Modern Climate Change and What the Future May Hold
Energy movement in Earth’s atmosphere
Let’s take a look at how energy moves in and around our planet Earth and its atmosphere. How is energy gained? We gain energy through the sun, with the amount of energy arriving depending on the time of day, time of year, cloud cover, air quality, and other factors. When sunlight reaches the earth’s surface, a large portion is absorbed, leading to a warming of the surface. Now, let’s consider how energy moves out of our system. Interestingly, the climate system doesn’t lose energy in the form of light, but rather in the form of heat. A large determining factor of how much is lost depends on the composition of our atmosphere, a subset of which is greenhouse gases.
Learn more about Greenhouse Gases and the Greenhouse Effect
A warmer atmosphere can increase rainfall
In a warmer atmosphere, the air can hold more water vapor. The implication is that, under warm conditions, we should get more precipitation when it rains. Details vary across data sets, but there is agreement regarding the large increase in statewide precipitation. According to the Illinois State Climatologist, total annual precipitation has increased by around 5 inches, 12%-15%, in the last 120 years, with most of the increase occurring during spring in southern Illinois and during the summer in central and northern Illinois. There has also been an increase in extreme precipitation events such as flash floods and other risks related to infrastructure (e.g., reservoirs).
Looking to the future: What climate models say
The significance of historical warming, both globally and in Illinois, raises concerns about our climate future and the choices that we must collectively make. For that, we rely on climate models. We start with complex computer models of the climate system that include the major components (atmosphere, oceans, land surface, ice, vegetation) and the exchanges that take place among them.
Then there is the unknown factor: future greenhouse gas emissions - a factor dependent on society’s response to the threat of climate change. Researchers produce scenarios based on the different levels of greenhouse gas emissions. On one hand, if we quickly reduce our emissions, we can limit atmospheric greenhouse gas concentrations and the amount of warming that occurs. On the other hand, if we continue to rely heavily on fossil-derived energy, we could experience as much as 4°C (>7°F) of warming during this century.
By looking at many different climate models, across many different scenarios and inputs, we can start to understand different possible climate futures. While projecting the future climate at the regional scale is challenging, several general statements can be made about the 21st-century climate of Illinois:
Illinois is likely to continue warming in the coming decades as large-scale warming continues. The rate of warming, and therefore the nature of warming-related impacts, is highly dependent on global greenhouse gas emissions.
It is also very likely that the increase in precipitation will continue accompanied by more precipitation variability (e.g., drought).
We expect to see an increase in extreme events, particularly precipitation events, driven by the increase in atmospheric moisture.