paleoclimate

Yes, climate change is real—and we’re causing it

Especially in the news as of late, there has been a lot of talk as to whether politicians “believe” in climate change. Framing the question like this makes it seem as though climate change is in the league of Santa Claus or the Easter Bunny—things that require belief for their existence. However, climate change doesn’t care whether or not we “believe” in it. Much like how the Earth is round, climate change is something that is regardless of how we feel about it. Global climate is warming, and we’re the ones that are directly responsible.

So how do we know that global climate has drastically warmed? Drilled ice cores from Antarctica yield CO2 records that serve as a proxy for global temperatures back in the geologic past. (Read more about paleoclimate proxies here.) Over the past 400,000 years, these ice cores show that CO2 values ranged from around 180 to 300 ppm, with the variability tracking glacial-interglacial cycles. In the late 1950s, the Mauna Loa Observatory began taking direct measurements of CO2 in the atmosphere. From this time to the present, COvalues skyrocketed. Today, they are now off the charts and have surpassed 400 ppm. This is a drastic, unprecedented and indisputable rise in CO2 values and global temperature, and it has been directly caused by human activities.

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CO2 values over the past 400,000 years to present. Image source: NASA

We can compare this trend in rising CO2 values to modeled CO2 trends if only natural forcings—orbital changes, volcanoes and solar effects—were at work. Over geologic time, these natural forcings have been important drivers of changes in CO2. However, as the graph below clearly shows, natural forcings at work today do not match the increase in CO2 values over the last century. Instead, natural forcings alone would support no changes in CO2 and global temperature.

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However, if we instead look at only anthropogenic (human) forcings and the observed increase in CO2 concentrations, we begin to find a much clearer correlation. While land use, aerosols and ozone alone would actually stabilize or even decrease COconcentrations, greenhouse gas emissions follow—and even surpass—the observed CO2 trend. It is these greenhouse gases, emitted by humans, that are the primary driver of global warming.

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Collapse all these anthropogenic factors together, and now you have have a trend that tracks along well with the increase in CO2 concentrations over the last century.

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Include in the influences from both natural and anthropogenic forcings, and the trend even more closely matches the directly measured increase in CO2 concentrations and global temperatures.

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Based upon these individual components, greenhouse gases emitted by humans are directly responsible for climate change. CO2 concentrations show annual fluctuations based on when vegetation is “inhaling” or “exhaling” CO2, but the overall increase is indisputable. Strategies and policies to mitigate and adapt to climate change are needed immediately. As global temperatures continue to rise, continental ice sheets will melt and raise sea level, arid areas will become even more prone to droughts and national security concerns will reach new heights.

It is a small bit of comfort to know that the Earth is going to be just fine at the end of this. Over its 4.5 billion year history, the Earth been through a lot—meteorite impacts, massive volcanic eruptions, continental collisions, etc.—and it has come out just fine. However, it’s humans and the biosphere that will directly be at risk. If we don’t soon mitigate or reverse the effects of global warming, humans may find themselves victims of a sixth mass extinction.

So instead of “do you believe in climate change?”, questions now need to be, do we accept that climate change is an important issue? How are we going to mitigate or reverse its effects? Are we even aware of how severe its effects may be? Every time a politician denies the reality of climate change, they are putting all of us at risk. So please share this with your friends and family, write to or call your state’s government representatives and urge them to act upon the reality of climate change. The fate of humanity and the biosphere quite literally depends on it.

Global warming graphs adapted from Bloomberg and NASA

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