Negotiators in Paris are trying to craft a deal at the UN climate talks that will keep global temperature rise below 2C. But what does that mean in reality - and what difference will a couple of extra degrees really make?

Without action, climate scientists have warned that temperatures could rise by nearly 5C above pre-industrial levels by 2100. World leaders meeting in Paris hope to keep average global surface temperature rises below 2C – but their pledges to cut emissions could still see up to 3C according to analyses. While it is very hard to make firm predictions, here are some of the potential impacts. All are for possible temperature rises occurring by 2100.

1C – 2015 was the first year to reach this level





2C

Many species and ecosystems with limited ability to adapt to higher temperatures will be subject to “very high risks” even with 2C of warming.

At particular risk are species dependent on Arctic sea ice – such as polar bears – and coral reefs.

Warming of around this level would see global annual economic losses of 0.2-2% of income, though experts caution that the “global economic impacts from climate change are difficult to estimate”.

Arctic sea ice extent in September falls by 43% in extent against the long-term average.

Snow cover in the northern hemisphere spring decreases by 7%.

Sea levels rise by up to 55cm. They have already risen by around 20cm over the 20th century.

The oceans get more acidic, with the surface ocean pH decreasing by 15-17%.

Glaciers decline in global volume by as much as 55% (excludes those on Antarctica’s periphery and the Greenland and Antarctic ice sheets).

1.5 billion people exposed to heatwaves each year.

30 million people affected by flooding each year.

1.5 billion people exposed to increased water stress.

3C

Negative impacts on production of major crops including wheat, rice and maize, in tropical and temperate regions.

However, some individual locations may actually benefit.

Most small mammals without high ground to escape to will not be able to keep up with the rate of climate change.

5.7 million sq km of cropland decline.



4.5 billion people exposed to heatwaves each year.

60 million people affected by flooding each year.

1.75 billion people exposed to increased water stress.



Ocean acidification is much greater, with surface ocean pH decreasing up to 62%.

Above 4C

Snow cover in the northern hemisphere spring decreases by 25%.

The Arctic is nearly ice-free in summer, as early as 2050.

Food security faced with large risks globally.

Sea levels rise up to 82cm.

Ocean acidification accelerates hugely, with surface ocean pH decreasing up to 109%.

In regions that are already dry, drought frequency will likely increase.

Less rainfall likely in mid-latitude and subtropical arid and semi-arid regions.

But high latitudes and equatorial Pacific likely to see more rainfall.

Glaciers decline in global volume by as much as 85%.

Wildlife and ecosystems hit by “severe” and “widespread” impacts, with substantial numbers of species going extinct.

Hot and humid enough to compromise normal human activities such as growing food or working outdoors, in some areas for parts of the year.

Atmospheric circulation is affected, with mid-latitude jet streams shifting polewards by 1 or 2 degrees latitude in both hemispheres.

With over 5C of warming, 12 billion people would be exposed to heatwaves each year, 7.6 million sq km of cropland will decline, 120 million people a year will be affected by flooding, and 2 billion people will be exposed to increased water stress.

Sources: IPCC, Met Office

