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Hank: Nothing says Friday like a hard-hitting report on climate change. A new and pretty serious climate change forecast came out this week in the journal Nature Climate Change, and it suggests that there's a 95% chance the earth's average temperature will increase more than two degrees Celsius this century. And that isn't great news, but there might still be time to stop it.

When you hear scientists talking about limiting climate change, you usually hear something about how we shouldn't let the earth warm by more than two degrees Celsius. What they mean by this is that we should make sure that, this century, the earth's average temperature doesn't get more than two degrees hotter than pre-industrial levels, or the average global temperature before the late 1800s, which was around 14º Celsius.

Now a couple of degrees might not seem like a lot, especially because weather changes by more than that all the time, like day-to-day, but the average global temperature usually is really stable and doesn't change by more than a degree or so. Two degrees is generally considered the major benchmark because that would be enough of a temperature change to have serious long-term impacts on human life. It would lead to things like flooding, extreme heat waves, and droughts, which would make it harder for us to grow enough food, among other problems, as if that wasn't enough.

But even keeping global warming under two degrees isn't really enough because rising sea levels would be a problem for a lot of small island nations, so there's like a stretch goal of 1.5 degrees. Unfortunately, we're already one degree warmer than pre-industrial levels, so we don't have a lot of wiggle room. And on top of that, this new study isn't too optimistic.

After doing a lot of statistics, researchers suggest that there's only a 5% chance the earth won't warm by more than two degrees by 2100, and only a 1% chance we'll meet the more ambitious 1.5 degree goal.

Instead, we're looking at in increase of between two and five degrees, meaning heat waves, droughts, storms, and rising sea levels will all become a lot more severe. Everything from the quality of our air to the price of our food will be affected, and those changes will get harder to reverse the higher the temperature gets.

Now the results of this study aren't surprising. They're more or less in line with the results of previous analyses, but they show that we're closer to the brink than we like to believe. The statistics for this new study were based on three factors: world population, per capita gross domestic product, or GDP, which measures a country's economic output per person, and carbon intensity, which is the amount of carbon dioxide emitted for every dollar a country generates. The data were based on trends from the past fifty years, including new United Nations projections for the world population. The UN numbers predict that the earth's population will be about 11 billion people by 2100 and that most of that increase will be in sub-Saharan Africa.

But those countries use much less fossil fuel than the rest of the world, and even by 2100, they're expected to contribute only about 6% of the world's CO₂ emissions. So population growth will probably have a small effect on greenhouse gas emissions. It isn't really a great idea for countries to start cutting their GDP either, so if we want to lower greenhouse gas emissions, the main thing to focus on is carbon intensity.

Thanks to new emissions standards around the world, carbon intensity should decrease by about 1.9% per year, which is a great start, but that will not be enough to stop the planet from warming more than two degrees, and how fast carbon intensity continues to drop will determine our future.

Right now, there's a wide range of possible carbon intensities over the next century, but what actually happens will depend on technological advances and environmental regulations. The forecast may not look great right now, but it's important to remember that this study doesn't mean the planet will absolutely, definitely warm by more than two degrees by 2100. The researchers say the two degree goal might still be possible, in their words, with "major, sustained effort."

So we've got a lot of work to do in the next 80 years, especially, I gotta say, all the scientists and engineers out there, making this stuff happen.

Thanks for watching this episode of SciShow News. If you would like to learn more about climate science and what some scientists think could help us out, you can watch our video about how to save the earth from us.

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