“We are facing at this moment the end of history for some of us…The difference for us between 1.5 and 2 degrees is whether to survive or to collapse.”

Those are the words of Antonio Lima, the small island country of Cape Verde’s ambassador to the United Nations, here at the international climate change negotiations in Cancun.  Cape Verde, along with over 40 other small island countries, will lose much of their nations to the sea as the water levels rise with climate change.

These negotiations are ultimately about nations cooperating to reduce global emissions of greenhouse gases that cause climate change and to address the impacts – but what exactly are the target level of emissions reductions the world is striving for?

No fun in the sun for Noah in Cancun

The U.N. Framework Convention on Climate Change (UNFCCC) states that its ultimate goal is to “prevent dangerous anthropogenic interference with the climate system.”  (In layman’s terms, to prevent humans from disrupting normal climate patterns in a potentially dangerous way.) It has been up to negotiators to assign this goal a number.  Last year, the Copenhagen Accord recognized that the “scientific view that the increase in global temperature should be below 2 degrees Celsius.”

It all depends on how you define “dangerous”

According to the latest science, and the impacts to small island states and other vulnerable countries, biodiversity and ecosystems, a 2 degree Celcius increase in global average temperatures is itself dangerous.  The planet has already warmed some 0.8 degrees C since preindustrial times and we are already seeing the huge loss of glaciers and sea ice, massive heat waves, stronger hurricanes, and more frequent and severe floods, droughts and fires.  It’s almost hard to imagine where we are heading.

Without action, we are heading towards a 3, 4, 5 or even 6 degree C increase in global temperatures.  When countries made individual pledges to cut emissions in Copenhagen last year, the U.S. pledged to cut emissions by 17% below 2005 levels.  This pledge, along with pledges from the other signers of the Accord came nowhere close to reaching the target of limiting global warming to 2 more degrees C.

So it’s hard to imagine a global agreement that meets the 2 degree goal – and scientists are even warning that that target is too high. Which brings us back to the statement by Ambassador Lima from Cape Verde, calling for a 1.5 degree world – not a 2 degree world.

If your head doesn’t hurt from the different numbers yet…

For most of human history, the concentration of carbon dioxide in the atmosphere was about 275 parts per million, or ppm.  After 200 years of increasing greenhouse gas pollution, humans have raised that concentration to over 385 ppm.  To limit global warming to 2 degrees C, the concentration needs to be limited below 450 ppm.  To reach the 1.5 degree target – the one scientists suggest is needed to prevent ecological tipping points and catastrophic sea level rise – the concentration needs to drop to 350 ppm.

That actually means the world can’t just slowly ratchet down emissions – we actually have to reduce the concentration in the atmosphere.

A daunting task, but here in Cancun there is momentum to push for the 1.5 degree target.

(That’s it for numbers for now!)

Learn more:

Read more from Noah in Cancun this week!

See how climate change is already impacting wildlife across the United States with our interactive map.