01 Climate science is not new. And it most definitely is not a 21st century trend that will go away on its own.
Progress in climate sciences dates back 200 years. As early as 1824, Jean Baptiste Fourier calculated that the average temperature of Earth should be much colder than observed. He reasoned that the atmosphere must absorb some infrared radiation from the Sun and Earth and emit it back to the planet’s surface.
In 1896, Svante Arrhenius published a paper predicting that if we ever doubled the concentration of CO2, the average surface temperature of the planet would rise between 5 and 6°C, a number he revised downward to 4°C in 1908.
02 Water vapor and carbon dioxide are both greenhouse gasses that trap heat near Earth's surface, but why are we so focused on carbon dioxide?
If we were to magically double just the amount of water vapor in the atmosphere, in roughly two weeks the excess water would rain and snow back into oceans, ice sheets, rivers, lakes, and groundwater. Because water vapor leaves the atmosphere so quickly, extra vapor doesn’t have much of a long-term warming effect.
But if we were to instantly increase the concentration of CO2, it would take roughly 100 years for about half of it to cycle back into plants and the ocean. The other half? Thousands of years. This is why long-lived greenhouse gasses like carbon dioxide have an important influence on Earth’s climate.
03 How much of the CO2 increase is natural?
Take a look below at the history of atmospheric CO2 and Antarctic temperature going back 800,000 years, thus covering many Milanković cycles. Clearly, the atmospheric concentration of CO2 does vary naturally, in tandem with temperature, ranging from about 180 to about 280 parts per million by volume (ppmv). But the Milanković cycles cannot account for the enormous spike at the end of the record, a spike to over 400 ppmv that humans put there. There is no evidence that it has been that large for many millions of years. If we do nothing, and there is no global economic meltdown, we may reach well over 1000 ppmv by the end of this century. This is not natural.
04 By the end of the century, we could see CO2 concentrations not seen for 50 million years.
This was when alligators roamed Greenland and sea levels were 230 feet higher than today. Unless humanity makes substantial changes in emissions or their capture, by the end of the century we could see CO2 concentrations not seen for 50 million years.
Additionally, if nothing is done to curb emissions, and economic growth proceeds rapidly in the developing world, by 2100, global mean temperature may rise between 2.5 and 4.5°C (that’s 4.5 to 8°F), and by 2300, by between 4 and 13°C (that’s 7 and 23°F).
05 How long can we wait to act?
Unfortunately, waiting much longer to see which way things go is not a viable option since it takes thousands of years for CO2 levels in our atmosphere to decline once emissions stop. In fact, even if we were to magically cut all emissions today, we would still see CO2 levels of over 400 ppm until the year 3000. By the time the consequences of climate change become unequivocally clear, it will almost certainly be too late to do much about it.
06 Broadly speaking, there are three strategies: reduce greenhouse gas emissions, compensate through climate engineering, and adapt to climate change.
We can reduce emissions by converting to renewable energy. The growth in solar and wind power in recent decades has been truly impressive. And the price of these energy sources has fallen as demand increases and technology improves. Another mitigation strategy is to reduce the effect of emissions by capturing and storing their greenhouse gas components.
Geoengineering seeks to actively counter greenhouse gas-induced warming. A popular technique involves injecting modest amounts of sulfur into the stratosphere, resulting in the formation of sulfate aerosols that reflect sunlight and thereby cool the climate system. The technology to do this pretty much exists today, and the cost of doing so is small enough that a small nation or even a wealthy individual could pull it off.
Nations will need to adapt to climate change, entailing measures ranging from crop substitutions to beefing up seawalls and levees and planning for shifting demands for and supplies of water and food.
07 The bottom line
There is overwhelming scientific evidence that the majority of the rapid warming of our planet over the past century has been caused by increasing greenhouse gas concentrations. Science suggests that we may be able to avoid the greatest risks of climate change by removing carbon emissions from our world’s energy supply very soon, within the next 10-15 years.
And there are many reasons to be optimistic that we can do this. We can scale carbon-free energy sources, technology for capturing CO2 from power plants and industry, and ways to extract CO2 directly from the atmosphere. Renewable energy can power 20%-60% of current energy needs, and more if better energy-storage technology is invented.