Reports - Constrain

Zero in on remaining carbon budget and decadal warming rates

ZERO IN Report 4

Our fourth ZERO IN report looks at how cutting emissions in this critical decade for climate can limit temperature rise and other climate impacts in the near-term. In doing so it provides supporting information on the latest IPCC reports, unpacking the level of action needed to slow down and even halt warming in the coming decades, in line with the Paris Agreement. It also shows how increased ambition and action can limit the worst climate impacts, from floods and cyclones to heatwaves, across the world.

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Download Graphic Figure 1 FIGURE 1: Warming per decade up to 2050 of selected illustrative pathways (sustainable development – SP; low energy demand – LD; renewable energy – Ren; gradual strengthening of current policies – GS; and the reference pathway for moderate action – ModAct).
Download Graphic Figure 2 FIGURE 2: Examples of climate impacts in 2050 as a result of three different global warming levels (blue: 1.5°C; orange: 1.7°C; pink: 1.8°C) in different countries.
Download Graphic Figure 3 FIGURE 3: Central remaining carbon budget estimates for a 50% chance of staying within 1.5°C warming, based on different methodologies, compared to future emissions from planned and existing fossil fuel infrastructure from 2020.
Download Graphic Figure 4 FIGURE 4: Timeline of key science and policy processes. Upper panel: processes under the UNFCCC relating to the Global Stocktake (GST) and NDCs; lower panel: IPCC releases of the AR6 cycle and potential release dates of the main reports of the upcoming IPCC AR7 cycle.
Download Graphic Figure 5 FIGURE 5: Global temperature increase in 2050 compared to pre-industrial levels (1850-1900) of selected illustrative pathways (left panel) and CAT scenarios (right panel).

ZERO IN Report 3

Our third ZERO IN report shows how the chances of global temperature rise staying within 1.5°C this century could range from around 75% to less than 30%, depending on how the climate system responds.

We therefore need to look at the range of temperature projections provided by climate models, rather than just single best estimates, when assessing our chances of keeping warming below a certain temperature. This doesn’t mean that it will be harder to stay within 1.5°C than we thought – instead, it shows that, alongside different emissions pathways, complex climate processes could lead us to different climate futures.

The overall message is that, instead of focusing on a single estimate of future temperature change, we need to prepare for a range of eventualities. The more we are aware of these eventualities, the better we can plan for what lies ahead.

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Download Graphic Figure 1 Warming contributions relative to pre-industrial levels (1850-1900) from groups of anthropogenic drivers, i.e. CO2 , non-CO2 greenhouse gases including CH4 , aerosols and land-use reflectance, for all five illustrative emissions scenarios assessed by IPCC AR6 WGI for 2020-2050.
Download Graphic Figure 2 Average decadal warming rates over the next 20 years (2021-2040) by groups of anthropogenic drivers, i.e. CO2 , non-CO2 greenhouse gases including CH4 , aerosols and land-use reflectance, for all five illustrative emissions scenarios assessed by IPCC AR6 WGI. Bars represent the central estimates, whiskers (dark blue) show the very likely (5-95% model) range.
Download Graphic Figure 3 Annual fossil & industrial CO2 emissions and projected global mean temperature trajectory, central estimate and very likely (5-95% model) range, relative to pre-industrial levels (1850-1900) of the original MAGICC7 climate emulator experiment before changing the model ECS and aerosol forcing by ±10% and switching off permafrost feedbacks. Model setup and emissions scenario specifics are based on Nicholls (2021).
Download Graphic Figure 4 “Climate wheels” showing the probabilities of staying below 1.5°C, 1.75°C, 2°C, 2.5°C, and 3°C in the 21st century for the different MAGICC7 experiments (±10% Equilibrium Climate Sensitivity (ECS), ±10% aerosol forcing strength, permafrost off) under the same stringent emissions reduction pathway that reaches zero fossil and industrial CO2 emissions around 2050.
Download Graphic Figure 5 Comparison of 21st century global mean temperature change for concentration- and emissions-driven emulator runs under the same very low emissions scenario (SSP1-1.9). Central estimates and very likely (5-95% model) ranges are provided for the near-term (2021-2040), mid-term (2041-2060), and long-term (2081-2100) relative to the recent reference period 1995-2014. The IPCC AR6 WGI Chapter 4 assessment as well as concentration-driven estimates shown in darker shading, emissions-driven estimates in lighter shading. Figure based on IPCC AR6 WGI Cross-Chapter Box 7.1 Figure 1.
Figure 6 Animated “climate wheels” showing the probabilities of staying below 1.5°C, 1.75°C, 2°C, 2.5°C, and 3°C in the 21st century for the different MAGICC7 experiments (±10% Equilibrium Climate Sensitivity (ECS), ±10% aerosol forcing strength, permafrost off) under the same stringent emissions reduction pathway that reaches zero fossil and industrial CO2 emissions around 2050.

ZERO IN Report 2

Our second report zeroes in on a new generation of climate models, known as CMIP6, and the science behind the Paris Agreement's Long Term Temperature Goal (LTTG), highlighting how improved understanding in both areas can help us to better plan for what lies ahead in terms of our future climate.

We also highlight the effect of COVID-19 on climate - although this has so far been negligible, a green recovery could profoundly alter the trajectory of climate change over the next two decades, both slowing down the rate of global warming and getting the world on a 1.5°C pathway.

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ZERO IN Report 1

This first CONSTRAIN report zeroes in on the remaining carbon budget as well as projected surface warming rates over the next 20 years. Both topics are vitally important to the implementation of the Paris Agreement.

Future reports, to be published annually, will provide further information on crucial scientific concepts relevant to the Paris Agreement, as well as background and context on new developments that relate to the science-policy interface.

The downloadable graphics are also presented within the report, alongside a full description.

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Figure 1 Figure 1 A schematic representation of the methodological approach used to derive the remaining carbon budget and related uncertainties, based on Rogelj et al. (2019)
Download Graphic Figure 2 Figure 2 Overview of value judgements and climate science components determining the size of the remaining carbon budget.
Download Graphic Figure 3 Figure 3 Global surface air temperature change per decade for the 2020-2040 (near-term) reference period under three Shared Socio-Economic Pathways (SSP1-1.9 [green]; SSP1-2.6 [orange]; SSP5-8.5 [blue]) and current nationally determined contributions (NDCs [grey]), as derived from the FaIR simple climate mode (box plots) and the CMIP6 model-average ensemble (filled dots).
Download Graphic Figure 4 Figure 4 Examples of forcing adjustment mechanisms, adapted from Sherwood et al. (2015)
Download Graphic Figure 5 Figure 5 Overview of historical ECS estimates. p denotes probability. Figure credit: Thorsten Mauritsen (CONSTRAIN).

Publications

ZERO IN Report 4

ZERO IN Report 3

ZERO IN Report 2

ZERO IN Report 1