5.4 What is the relationship between emissions now and climate change in the future?

The range of future climate change is constrained within quite narrow margins between now and 2030, because:

• we are committed to change as a result of past emissions (the world would continue to warm by 0.6°C even if all emissions attributed to human activity were to stop immediately)

• interactions between various forcing factors related to emissions into the atmosphere (some of which have negative effects but have short residence times) mean that there's a time lag between emissions of greenhouse gases and their effect on climate.

Current emissions will impact on climate from 2030 onward, so the level of climate change beyond 2030 depends crucially on the rate at which global emissions decline from now on.

From 1970 to 2000, global average mean surface temperature increased by 0.6°C, and will increase by a further 0.6°C by 2030.

On current trends and projections a ‘global average temperature warming of between 1.8°C and 4°C over 1990 levels by 2100, depending on the level of emissions, but warming of up to 6.4°C is possible’ (UK Government response to the recommendations of the CCC – see below).

If temperatures rise by 4, 5, 6°C or more by 2100, then that increase will be dramatic – all within 70 years from 2030 (but increasingly non-linear).

• Briefing on future temperature change from the US Environmental Protection Agency.