The greenhouse effect is a consequence of certain gases present in the atmosphere, trapping heat emitted by the Earth, much like the glass walls of a greenhouse. Greenhouse gases retain heat, causing a rise in temperatures, crucial for sustaining life on Earth. However, human-induced emissions of these gases have become a severe problem.
To comprehend the greenhouse effect, it's essential to understand how energy enters and exits the Earth and its atmosphere. Sunlight, in the form of high-energy solar radiation, is the primary energy source. Reflective surfaces, clouds, and the atmosphere absorb and reflect incoming solar radiation, with the Earth converting absorbed energy into heat. Greenhouse gases in the atmosphere then trap and re-emit heat, contributing to a temperature increase.
Carbon dioxide (CO2), a well-known greenhouse gas, has naturally cycled in and out of the atmosphere for billions of years. However, human activities, particularly burning fossil fuels, have caused a recent spike in CO2 levels. Since 1880, the average global temperature has already increased by 1°C, and by 2052, is likely to warm another 0.5°C, even if we take action now.
While nitrogen and oxygen, the most abundant atmospheric gases, have no greenhouse effect, certain gases, despite being a small part of the atmosphere, have a significant impact. Carbon dioxide, primarily from burning fossil fuels, contributes nearly 80% of the increase in greenhouse gas emissions. Ozone, produced by human-induced interactions in car and industrial exhaust, is a component of urban smog.
Carbon dioxide (CO2), the most familiar greenhouse gas, cycles in and out of the atmosphere naturally: it is absorbed by plants, for example, and re-released if the plants are burnt by a wildfire. But because carbon dioxide is produced when fossil fuels and biomass are burned, too, this gas is the major driver of anthropogenic climate change, contributing nearly 80% of the increase in greenhouse gas emissions between 1970 and 2010.
The most abundant greenhouse gas may surprise you: water vapor. Water's role in the atmosphere is complicated, given that air temperature has a direct effect on its presence. One worry is that warmer air can hold more water—launching a potential feedback loop, in which vapor leads to warming, which leads to more vapor. But there is a limit to how much water the air can hold; eventually, it will condense into clouds, which deflect incoming solar radiation. (And unlike most other greenhouse gases, water vapor stays in the air for a few days at a time.) Scientists are still working to understand these cycles, as well as how the concentration of water vapor may have changed over time.
The scary truth is that the greenhouse gases we've already emitted have had an impact that can't be undone: Already, the world is a degree warmer than it was before the Industrial Revolution—and is growing hotter still. Our goal now has to be to limit further warming as much as possible.
The Intergovernmental Panel on Climate Change wants to keep warming at or below 1.5°C. To get there, they say, our work is cut out for us: The world needs to hold the concentration of atmospheric carbon dioxide at its present levels, and decrease the concentration of other greenhouse gases.
That will require a rapid overhaul of the world's electricity grids, shifting to mostly renewable energy sources by 2050, perhaps accompanied by more controversial technologies like advanced nuclear power. And we will simply need to use less electricity, too. Industry will need to reduce its emissions by as much as 90% as compared to 2010 levels. As electricity gets cleaner, other energy consumers—like transportation systems—will need to electrify.
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