Radiation, Aerosols and Gases
Written by Neil McCabe
Scientists are in agreement on the essential science of climate change. It is clear that it is time to take action to halt the pace of Earth’s overheating. Climate models have demonstrated this, showing that the more greenhouse gases we throw up into the atmosphere the more Earth’s surface temperature increases. Climate models are predictions based on the physics of air and water on our planet as it rotates and its distance from the sun. The climate models have largely matched the actual observations from data collected. Using historic temperature records over the last 150 years, scientists have been able to show hikes in average global temperature, especially over the last 50 years. It is difficult to break down the different scientific aspects of climate change but I will attempt to do so in parts over the next few blog posts.
Every day Earth’s surface absorbs 67% of the sun’s “short wave” radiation. This radiation comes in direct form and travels through our atmosphere. It heats Earth’s surface, making it a warmer place to live. Earth emits 33% of its heat back out as “long wave” infra-red. Clouds and gases in the troposphere can actually capture and resist the heat being emitted and send that heat back down towards the area it came from. Thus, the natural greenhouse effect occurs. But without this abundant direct radiant heat, Earth would be -18˚C and not an easy place to live.
Higher temps come from many sources but the biggest problem we are faced with now is the threat of increased carbon dioxide (CO2) and its equivalents (CO2e) resting and mixing in Earth’s atmosphere. These gas emissions are manmade and they sit like a blanket over land and trap the heat being released from Earth as surface radiation / outgoing longwave radiation. This is the non natural greenhouse effect.
In other words, the sun heats the Earth. Earth warms up and sends some of that heat back up to the atmosphere, where the heat gets trapped by the clouds and gases. A lot of these gases are not meant to be there and have only been there for the last 200 years. The trapped heat is sent back down to Earth. This is not good for us over the next several decades.
Aerosols and Gases - good and bad
Gradually more heat is staying in the atmosphere and the same amount of solar radiation is entering the atmosphere, both at the same time, so that there is an energy balance at the top of the atmosphere. The gases reflecting the heat also hold aerosols that we are responsible for creating. Aerosols are tiny particles, dust-like in composition. Without human interference they were traditionally not that bad. They break up and fall back to Earth after only a few days assisted by precipitation, and actually help reflect incoming solar radiation. However, mining, fracking, gas production and deforestation are pumping out aerosols at an alarming rate.
Our problem is that we are pumping out greenhouse gases on a major scale. Burning fossil fuel to provide energy, coupled with the effects of major transportation and deforestation causes a rapid increase in global temperatures. The two main gases in the Earth’s atmosphere are Oxygen (O2) and Nitrogen (NO2). These gases have almost no effect on the greenhouse effect because they don’t absorb the solar energy reflected as long wave radiation from the Earth. Water Vapour (H20) and Carbon Dioxide (CO2) are the important natural greenhouse gases though they are less common than Oxygen (O2) and Nitrogen (NO2). Without them Earth’s average surface temperature would be a very cold -18˚C, so they are very important to life on Earth. However, the sudden addition of extra human-caused CO2 and other greenhouse gases is trapping more heat and causing rapid warming.
I’ll be talking about feedbacks, the direction Earth’s heat travels in, rising sea levels and melting ice in the next blog.