Carbon dioxide
Oil
Coal
Deforestation
How nature is key to achieving a 1.5˚C world
GHGs are the gaseous constituents that trap heat in the atmosphere. They are released through natural processes (e.g. decomposition of biomass) and as a result of human activity (e.g. the burning of fossil fuels). Some gases are naturally occurring (e.g. carbon dioxide) while others are human-made (e.g. the halocarbons). Carbon dioxide (CO2) is the largest single contributor to climate change. The United Nations Framework Convention on Climate Change covers the following GHGs:
Carbon dioxide
Oil
Coal
Deforestation
Methane
Cattle
Fertilizer
CFCs & Haloalkane
Refrigerators
Aerosols
Nitrous oxide
Gasoline
Agriculture
The three main systems capable of storing carbon and nitrogen, known as “stocks” or “pools”, include the land ecosystems, the ocean and the Earth’s crust.
Carbon and nitrogen not stored in these pools resides in the atmosphere as a component of greenhouse gases.
For example, forests are the largest terrestrial sink - globally, their net removal of carbon is equivalent to 5.7 billion metric tonnes of carbon dioxide (GtCO2) a year. This represents 45% of carbon dioxide sequestration from the land sink.
This is already happening in forest areas across the tropical belt…
This map shows the net carbon sinks (green) and sources (red) from forests across the period 2001-19 (MtCO2e). The largest sinks are found in tropical forests. The largest sources are found in disturbed tropical forests.
Emissions from human activities on land, including those leading to land-use change and forestry (LULUCF emissions) are often cited as accounting for 10-15% of global CO2 emissions (~38.5 GtCO2).
But by focusing on net CO2 fluxes, this approach underplays the significance of the land sector in climate mitigation.
Considering non-CO2 gases and looking at the gross fluxes instead of net emissions, the contribution of the land system to climate change is startling, representing 48% of all anthropogenic GHGs flowing in and out of the atmosphere.
Annual emissions and removals for carbon (average 2010-19), methane (av. 2008-17)
and nitrous oxide (2007-16), GtCO2e.
Climate change will significantly impact our society’s production systems, vital economic and social infrastructures, government facilities, threatening our jobs and livelihoods.
The frequency of disasters, the survival of plants and animals, the spread of diseases, the stability of our global climate system and – ultimately – the possibility for humanity to survive on this planet hinge on these few degrees.
The Paris Agreement signatories committed to keep global warming well below 2˚C above pre-industrial levels and pursue efforts to limit it to 1.5˚C. Even with 1.5˚C of warming the world will face severe climate impacts, but these get significantly worse with 2˚C.
Scientists are increasingly concerned about the existence of tipping points (defined as “critical thresholds beyond which a system reorganizes, often abruptly and/or irreversibly”) linked to a number of “Earth system feedbacks”.
For example, increased GHG concentration in the atmosphere leads to warming, which in turn results in reduced rates of carbon sequestration by the land and ocean sink (for example, either by causing wildfires or by reducing the rate of photosynthesis in plants) which further accelerates the change in atmospheric GHG concentration and climate.
Latest research suggests that rising temperatures could lead to a near halving of the land sink strength due to reduced photosynthesis by as early as 2040.
While the latest carbon budget – as set out in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change - takes into account a number of these Earth system feedbacks such as permafrost thawing, there is a high degree of uncertainty, meaning the remaining carbon budget could be overestimated. Recent research suggests that the budget for remaining below 1.5˚C has a 17% chance of already being negative (i.e. we have already surpassed it).
To reduce the risk of triggering these ecological and climate tipping points, we must reduce emissions as rapidly as possible and protect and enhance the remaining natural carbon sinks.
A bottom-up assessment of the Nationally Determined Commitments provided by countries as of May 2021 shows that a substantial ambition gap remains based on the levels of net emissions expected in 2030.
Achieving net zero emissions by 2050 (and thus keeping within 1.5˚C) requires all
governments and companies to raise their ambitions.
Average annual feasible and cost-effective (< $100/tCO2e) emissions reduction potential in the AFOLU sector, per reduction strategy between 2020 and 2050 (GtCO2e/yr)
GHGs can be removed from the atmosphere with biological or engineered chemical processes and stored for long periods of time in the ground, ocean or built environment.
These human engineered negative emissions technologies will undoubtedly complement nature-based removals but their costs are much higher, their potential for mitigation is highly uncertain, they lack co-benefits associated with wider SDGs and they have the potential to drive further inequality and wealth concentration.
In fact, at least 260 billion tonnes of irrecoverable carbon (GtCO2) are stored in ecosystems highly impacted by human activities around the world, particularly in peatlands, mangroves, old-growth forests and marshes.
Irrecoverable carbon means that, if released, it would not be possible to recapture that carbon on a timeframe relevant to meeting the target of zero net emissions by 2050 and maintaining temperatures below 1.5°C.
This carbon is highly vulnerable to release into the atmosphere as a result of human management/ use of land.
The most tried and tested method for
capturing carbon dioxide from the
atmosphere is the one the planet has been
utilising for millions of years: photosynthesis.
As a result, “natural climate solutions” are
expected to provide the lions share of carbon
removal in the next 30 years.
Natural climate solutions (NCS) are the activities that reduce land and marine emissions and protect and enhance land and marine removals.
NCS are defined as: conservation, restoration, and/or improved land and ocean management actions to increase carbon storage and/or avoid greenhouse gas emissions across global marine ecosystems, forests, wetlands, grasslands, and agricultural lands.
* Blue carbon ecosystems are defined as the vegetated coastal and marine ecosystems that sequester and store carbon (e.g. mangroves, salt marshes, and seagrass beds)
The ocean is a major regulating force in the Earth’s climate system, capturing slightly less than 1/5 of anthropogenic CO2 emissions per year.
But greater concentrations of CO2 also contribute to a rise in ocean acidification which results in negative implications for marine ecosystems, and the effect of ecosystem changes on the CO2 absorbed by the ocean is unknown.
If the risk of acidification were mitigated, significant opportunities could be developed to enhance ocean-based removals, through:
blue carbon projects: actions to enhance the capacity of vegetated coastal and marine ecosystems that sequester and store carbon (e.g. mangroves, salt marshes, and seagrass beds).
ocean fertilization: applying nutrients to the ocean to increase photosynthesis and sequester carbon.
ocean alkalinity: increasing ocean concentration of ions like calcium to increase uptake of CO2 into the ocean, and reverse acidification caused by enhanced CO2 uptake.
While blue carbon projects could reach a strong mitigation potential in 2050 (0.5-1.4 GtCO2e per year), ocean fertilization and alkalinity have highly uncertain feasibility and environmental impacts at this stage.
As such, we focus here on land-based or "terrestrial" NCS which can also deliver critical outcomes relating to climate adaptation and resilience, biodiversity and sustainable development.
CO2 sequestration through photosynthesis is the most cost-efficient and oldest carbon removal technology on Earth.
Forests play an essential role in regulating climate and water cycles, protecting against flood, drought and erosion, and maintaining soil and water health.
Mangrove forests provide more than $80 billion per year in avoided losses from coastal flooding and directly protect 18 million people in coastal areas. They also contribute $40–50 billion annually through fisheries, forestry and recreation benefits.
They are also highly cost-effective forms of mitigation, especially when it comes to removing carbon, with the potential to sequester 1.2 GtCO2 for under $30 per tCO2.
Method | Annual cost & mitigation potential |
---|---|
Afforestation, Reforestation & Forest management |
|
Wetland, peatland and coastal habitat restoration |
|
Soil carbon sequestration |
|
Biochar |
|
Bioenergy with carbon capture and storage |
|
Bioenergy with carbon capture and storage |
|
Building with biomass |
|
Method | Annual mitigation potential1 |
---|---|
Enhanced terrestrial weathering |
|
Mineral carbonation |
|
Ocean alkalinity |
|
Direct air capture and carbon storage |
|
Low-carbon concrete |
|