If you’ve had your finger on the pulse on the climate change debate, you’ll probably have heard the temperature of 2 degrees thrown around a lot. But what is it referring to? And what is the significance of this number?

If you were to type the term into Google, you’d most likely be greeted with a New Zealand-based mobile phone network and a sustainability consultancy of the same name. But in this instance, the 2 degrees phenomenon is referring to the warming threshold on the planet by the end of the century, to avoid some pretty dicey climate scenarios. That’s an average global rise of 2 degrees on pre-industrial levels. Why 2 degrees you ask? Well, quite simply, humans haven’t lived in a world that’s any warmer...

The idea dates back to 1977, when Yale economist William Nordhaus said: “If there were global temperatures more than 2C or 3C above the current average temperature, this would take the climate outside of the range of observations which have been made over the last several hundred thousand years.” Since then, the 2 degrees ceiling has been supported by a growing body of research, and adopted as a warming limit for the planet.

So if Nordhaus himself said 3 degrees, why not use that number instead? General consensus in the scientific realm finds that anything above 2 degrees can give way to some stormy times – quite literally. We could increasingly be at the mercy of some dangerous climatic events, from hurricanes and storms to floods and droughts. Not to mention the extinction of plant and animal species. The changes we may see could not only be catastrophic, but also irreversible.

Okay, so how about playing it safe and sticking to within a 1 degree rise in average global temperates? Unfortunately, it’s pretty improbable. Let’s put it this way: from 1880 to 2012, the world had already warmed 0.85 degrees. Yikes. So, 2 degrees is more achievable, if not still a highly ambitious target.

The 2 degrees ceiling has been supported by a growing body of research, and adopted as a warming limit for the planet

If you’ve read the news lately, you’ll probably read talk of the globe heating up by 4 degrees, and even 6 degrees. That’s because at the current trajectory of global warming, in a business-as-usual scenario, we’re more likely to hit these figures by 2100.

If you thought we had it bad with 2 degrees, imagine what we’ll be in for if that increment tripled. In fact, some scientists are describing a 6 degree world as one that is simply unimaginable to us. You can easily go from shivering in your boots at 8am to roasting in your summer jacket by lunchtime.

But as a global average, we’re looking at a world where deserts would expand, agriculture would be severely impacted and we’d be fighting over the scarce resources available. It’s something that UK science writer Mark Lynas compared to a meteorite hitting the planet, in terms of impact.

Before you tear your hair out in despair, change is on the horizon. Though emission-cutting on a global scale has all the haste of a rotating cruiseliner, companies and policymakers alike are taking action to curb those greenhouse gases.

In the political realm, governments agreed in 2010 that emissions need to be reduced to limit global temperature increases below 2 degrees. If you remember nothing else about climate change, remember this critical number – 2 degrees. After all, 3.6 Fahrenheit isn’t quite as catchy, is it?

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Read more from our content series as we explore everything you need to know about climate change (but were too afraid to ask) in the run up to Paris 2015!