Climate, Land-Use, and Ecosystem Services at 1.5C

Lead Research Organisation: UNIVERSITY OF EXETER
Department Name: Mathematical Sciences


In Paris last December, the world's governments agreed to pursue "efforts to limit the [global] temperature increase to 1.5 degrees C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change." More than half of the UNFCCC countries believe that a 2 degC warmer world would have impacts they couldn't cope with. Therefore, limiting climate change is extremely important for the livelihood of millions of people who live in climate-vulnerable regions around the world.

Scenarios considered in the IPCC 5th Assessment Report (AR5) that were designed to have a likely chance of staying below 2degC were only achievable with large-scale land-based mitigation. Land-based mitigation can include protection and enhancement of natural uptake and storage of carbon in vegetation and soils, as well as technologies to remove CO2 from the atmosphere. An example of the latter is bioenergy with carbon capture and storage. During combustion in power plants, CO2 can be extracted, transported, and stored in geologic repositories - this is the process of Carbon Capture and Storage (CCS). Combining bioenergy with CCS (BECCS) could result in negative emissions of CO2. BECCS is attractive since it results in a net removal of CO2 from the atmosphere while also providing a renewable source of energy.

However, large-scale land-based mitigation relies on increases in land area used for mitigation and increased productivity on existing land areas, adding pressure on food and timber production, availability of freshwater, fertiliser use and biodiversity. Our project will evaluate impacts of land-use changes for mitigation contributing to a 1.5 degC climate stabilization target. A key question is: Do the negative impacts of land use change (on food and water) outweigh the positive effects of avoiding some climate change? Land will certainly play a large role in reducing the amount of climate change we see this century - it comprises up to 25% of the total emission reductions promised by individual countries in the lead-up to the Paris agreements. However, these commitments alone are not enough to reduce climate change below 2 degC, so research into methods for increasing the reductions is urgently needed.

Our project brings together complementary expertise in climate, land-surface, and land-use modelling at the University of Exeter and the NERC Centre for Ecology and Hydrology, with first-hand knowledge of national and international policy on climate change and land-use change at the University of Bristol and the Government Office for Science. We will use various scenarios of future land use and climate change to quantify the potential for CO2 removal and inform emission budgets - how much CO2 we can emit while having a likely chance of remaining below 1.5 degC. It is essential that we limit climate change while also providing food and water for the growing global population. Therefore we will also generate scenarios and check final outputs for their ability to produce sufficient food to meet the expected increasing demand for high value foods higher in energy and protein.

Planned Impact

CLUES1.5 will provide an assessment of the environmental and carbon cycle impacts of a range of land-based mitigation scenarios that contribute to stabilising global mean temperature between 1.5 and 2.0 degC above the pre-industrial mean, the global goals agreed to by governments within the Paris Agreement. In Paris, governments further agreed on the need for improved scientific evidence around the feasibility and implications of meeting these goals, and requested the IPCC to produce a Special Report on 1.5 degrees and a Special Report on land (to cover "desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems"). This project will provide information of relevance to both reports, hence the significant potential impact of this project.

A clear pathway to impact is already laid out through peer-reviewed published science papers that can be included in the IPCC Special Reports. The primary outputs of CLUES1.5 will thus be papers on the overall impact of stabilization scenarios on food, water, and ecosystem services. We further plan to communicate the findings through a wide range of pathways that will include direct knowledge exchange based on extensive existing collaborations and relationships of project partners across national and international policy communities.

Impact beyond the lifetime of the grant will be facilitated by improvements to the JULES model, increasing its suitability for analysing land-based mitigation by adding bioenergy crop tiles; and the groundwork for a larger project looking at the optimal location and timing of land-based climate mitigation, potentially funded through the Greenhouse Gas Removal programme. The work of this and any future project can contribute to more detailed country-based analysis, useful for national decision makers in developing future Nationally Determined Contributions (NDCs), as well as scientific contribution to the IPCC 6th Assessment Report.
Description In this project we explored the land-climate-carbon cycle interactions in a new 1.5°C scenario (produced by the IMAGE group) that includes afforestation/reforestation/avoided deforestation and Biomass Energy and Carbon Capture and storage (BECCS), to remove CO2 from the atmosphere (Harper et al., Nature Communications, in review). We concluded that BECCS could be far less efficient for carbon dioxide removal than often assumed, and that as a result, BECCS is unlikely to deliver the substantial negative emissions required to stabilize at 1.5°C without significant overshoot. Harper et al. also argue that carbon removal though BECCS, which is assumed in most 1.5°C or 2°C scenarios, is uncertain because it strongly depends on underlying assumptions with respect to yields, land-use change emissions, and efficiency of CCS. In the IMAGE 1.5°C scenario, in order to meet the stringent requirements to stabilize at 1.5°C without significant overshoot, bioenergy crops are assumed to replace some natural forests at high latitudes. This is consistent with assumptions within IMAGE of high-yield bioenergy crops and efficient CCS, and that ~75% of the initial aboveground biomass is used for BECCS. However, we found that soil carbon emissions following the deforestation overwhelmed the carbon gains from bioenergy crops - significantly reducing the efficiency of BECCS. The loss of soil carbon in regions with high initial carbon density makes it difficult for BECCS to result in a net negative emission of carbon dioxide. In considering these ambitious climate targets, we therefore need to consider the net impact of the avoided climate change and the impact of the additional mitigation efforts required, i.e., a major challenge is to stabilize the climate well below 2°C, without mitigation options (such as BECCS) producing worse negative impacts than the additional climate change that they are designed to avoid.
Exploitation Route Results are summarised in a briefing for BEIS/DECC on the feasibility of the 1.5K target discussed in the Paris Accord, and are being fed into the IPCC Special Report on 1.5K.
Sectors Environment

Description Project is part of the NERC-BEIS funded programme on stabilisation of the climate at 1.5K above pre-industrial. Results of this project and two related ones (CLIFFTOP-CLUES-MOC1.5) were discussed in a workshop organised for BEIS and were fed into the IPCC report on 1.5K.
First Year Of Impact 2017
Sector Environment,Government, Democracy and Justice
Impact Types Societal,Policy & public services

Title Land-use and climate change for 1.5 and 2.0 degrees centigrade warming scenarios (JULES land surface model) 
Description This dataset includes six sets of model output from JULES/IMOGEN simulations. Each set includes output from JULES (the Joint UK Land Environment Simulator) run with 34 climate change patterns from 2000-2099. The outputs provide carbon stocks and variables related to the surface energy budget to understand the implications of land-based climate mitigation. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes