English: This image shows two graphs. The graphs show how global warming could be limited to below 2 degrees Celsius, relative to the pre-industrial level.

Greenhouse gas emissions

The graph on the left shows how global greenhouse gas (GHG) emissions (measured in carbon-dioxide equivalents, CO₂e) need to be reduced to around 20-25 gigatonnes (Gt) CO₂e per year, by 2050 (PBL, 2012, p.156). This is equivalent to a reduction in 2050 of between 40-60%, compared to 1990 emissions levels (PBL, 2012, p.157).

The graph shows how emissions are projected to grow in a trend scenario to 60-70 GtCO₂e per year, by 2050 (PBL, 2012, p.156). Under the trend scenario, global temperature in 2100 would increase by 2.5-5 °C (PBL, 2012, p.156). In other words, meeting the 2 °C target would require drastic emissions reductions compared to the trend scenario.

Contribution to cumulative emission reduction, 2010-2050

The graph on the right shows how the 2 °C target might be achieved. The graph shows three "pathways" to meet the 2 °C target, labelled "global technology", "decentralised solutions", and "consumption change". Each pathway shows how various measures could contribute to emissions reductions. These are:

• (A) avoid deforestation
• (B) reduce other (non-CO₂) GHGs
• (C) reduce other energy-related emissions
• (D) increase nuclear power
• (E) increase bio-energy
• (F) increase solar and wind power
• (G) increase CO₂ capture and storage
• (H) improve energy efficiency

For all three pathways, (B), (G) and (H) all make significant contributions to emissions reductions.

Below are the approximate contributions of (A)-(H) to the three pathways. Units are the percentage contribution to cumulative emission reduction between 2010-2050. The first number is the "global technology" pathway, the second "decentralised solutions," and the third "consumption change."

• (A) 14, 8, 13
• (B) 24, 25, 26
• (C) 3, 2.5, 2.5
• (D) 12, 1, 1.5
• (E) 8, 7, 8
• (F) 4, 12, 6
• (G) 20, 17, 18.5
• (H) 17, 27, 25