Summary

Forests have a very important role to play in global climate change mitigation. They act as carbon sinks while wood products offer alternatives to more carbon intensive materials and fuels. Forest Research reviewed previous studies that provide estimates for forestry-based mitigation options and highlights where further research is required in the future. Cost-effectiveness estimates are an important part of the evidence base needed to help the UK Government minimise the costs of meeting climate change mitigation targets.

Key findings and recommendations

• Methodological inconsistency and a lack of transparency hampers direct comparisons of estimates made by previous studies
• Forestry options are generally cost-effective compared to many other alternatives, as judged by current UK benchmarks
• Forestry options are critical – based on their relative cost-effectiveness, the significance of emissions from global deforestation, and the imperative to cut carbon emissions to limit the global average temperature rise in line with international commitments
• Incentives are weak for forest owners to implement mitigation activities – additional mechanisms, including payment for ecosystem service schemes, are needed
• More research is required – especially on the effects of afforestation on soil carbon balance, greenhouse gas balances for forest stands, carbon stock changes through a stand’s life cycle, the benefits of carbon displacement, and biophysical effects such as albedo and evapotranspiration
• For more information, see our video on the Low Carbon Summit – Incentives for Climate Change Mitigation by the Forest Sector – a UK perspective (Vimeo)

Publications

• Forestry Commission Research Note – Comparing the cost effectiveness of forestry options for climate change mitigation
• Research summary, detailed findings and recommendations
• Book chapter – How cost-effective is forestry for climate change mitigation?

Status

The project was completed in 2019.

Global carbon balances and climate change

Summary

Evidence from ice core data indicates that the current concentration of atmospheric carbon dioxide (CO₂) is unprecedented in the past 800,000 years, with data from boron-isotope ratios in ancient planktonic shells suggesting that it is likely to be at its highest level for about 23 million years.

Rise of carbon emissions

Anthropogenic carbon emissions rose by 70% between 1970 and 2004, from 29 to 49 thousand million tonnes of carbon dioxide equivalent (GtCO₂e) per year, with global emissions rising by 3% a year since 2000.

The current atmospheric concentration of CO₂ of over 390 parts per million (ppm), which is around two-fifths higher than the pre-industrial level of about 280 ppm, is currently rising at an annual rate around 2 ppm.

As atmospheric CO₂ concentrations have increased over the past 150 years, the mean global temperature has risen. In the absence of new policy action, annual world greenhouse gas (GHG) emissions could rise by a further 70% by 2050, and lead to a rise of 4 °C, or possibly 6 °C, above the pre-industrial global mean temperatures by the end of the century, with greater temperature rises likely in some regions, including the Arctic.

Impact of rising global temperature

Likely adverse impacts associated with exceeding a 1.5-2.5 °C temperature increase include increased risk of extinction of around 20-30% of plant and animal species, with many millions more people expected to be at risk of floods due to sea level rise by the 2080s.

Warming could lead to positive feedbacks that magnify temperature changes. These could include potential dieback of Amazon rainforest if warming exceeds 3 °C. Thawing of the permafrost and subsequent soil decomposition could lead to the further release of up to 380 GtCO₂e under a high warming (7.5 °C increase) scenario by the end of the century.

Recent evidence shows that warming of the Arctic is occurring faster than had been predicted, with sea level rising more rapidly than expected.

Preventing dangerous climate change

In order to prevent ‘dangerous climate change’, international agreements reached at Cancun and under the Copenhagen Accord call for limiting the average global temperature rise to no more than 2 °C above pre-industrial levels, with consideration of adopting a limit of 1.5 °C. To be confident of limiting the mean global temperature rise to between 2 °C to 2.4 °C, is thought to require stabilisation of atmospheric GHG concentrations in the 445 ppm to 490 ppm range, with reductions in annual global carbon emissions occurring no later than 2015, and emissions 50-85% below 2000 levels by 2050.

However, some scientists have argued that even the existing GHG atmospheric concentration, which, including the effect of other GHGs, is equivalent to around 430 ppm CO₂e, is too high for the temperature rise to stay below the 2 °C threshold.

Some have argued that the increase in atmospheric GHGs since pre-industrial times to date probably commits the world to a warming of 2.4 °C (1.4 °C to 4.3 °C) above the pre-industrial level during the current century, and have recommended a rapid reduction from the current concentration by around 10%.

Further information on climate change is available on the Met Office website.