- Estimates of the remaining global carbon budget (the overall amount of CO2 that can be emitted) indicate that rapid reductions averaging 2 gigatonnes of CO2 (GtCO2) (5% of 2020 global emissions) per year are required to keep global warming to within 1.5o°C. This pace of reductions must be maintained until net emissions are zero (around 2040).
- We may have already exceeded the carbon budget necessary to keep global temperature rise to within 1.5o°C of warming.
- If these unprecedented cuts in emissions are not made, we are likely to exceed 1.5o°C warming and require carbon removal technologies on an enormous scale.
- The short-term emissions drop during the COVID-19 pandemic had a very limited impact on the overall decarbonization towards meeting the 1.5o°C target.
- The power sector offers the largest opportunity for near-term decarbonization, but all economic sectors need to drastically reduce greenhouse gas (GHG) emissions (e.g. methane – see Insight 2).
In order not to exceed the 1.5oC maximum warming target, the remaining global carbon budget requires that annual global emissions reductions average 2 GtCO2 per year (coincidentally that’s close to the level of reduction in emissions in 2020 due to the COVID-19 pandemic of ~7% compared to 2019). Staying within 1.5oC warming also hinges on stringent reductions in emissions of non-CO2 greenhouse gases such as methane and nitrous oxide (which are further discussed in Insight 2).
While it may still be possible to stay within the carbon budget needed to remain within the 1.5oC target, it is highly unlikely unless unprecedented rapid and massive changes to the world’s economy and infrastructure are immediately undertaken. Supply side changes, such as shifting to renewable energy, need to be implemented alongside changes in demand. With continued progress in solar and wind energy technologies, additional low-carbon generation could soon be sufficient to meet new power demands if deployed in conjunction with demand-side reductions (which is further discussed in Insight 6). However, the residual emissions of existing and proposed carbon-intensive infrastructure, alone, are enough to exceed the carbon budget. Scrapping planned fossil-fuel based projects is therefore necessary. Additionally, early retirement of some economically viable but carbon-intensive infrastructure as well as deep reductions in every sector will be needed, employing all mitigation levers. By starting with a rapid shift to low-carbon electricity production, electrification of other sectors becomes a more viable option for also decarbonizing these sectors.
Deep societal transformation is needed to stabilize the climate at any temperature target and we have waited too long to start this process. Unless, beginning immediately, emissions are consistently reduced at an unprecedented scale, it will no longer be possible to keep warming within the 1.5oC target. In fact, most of the scenarios which include drastic action to stabilize global temperatures at the 1.5oC level, predict that temperatures will initially exceed that target, requiring unproven carbon removal technologies to be deployed on an enormous scale to make global emissions negative for many years. Exceeding 1.5oC even temporarily may have irreversible effects on oceans and other components of the Earth system as well as increasing the frequency of extreme events (see Insight 4).
- 440 – gigatons of CO2 that can be emitted from 2020 to stay within the 1.5oC warming threshold (50% probability)
- 2 – GtCO2 yearly reduction in emissions needed to stay within that budget
- 10 – remaining years until the budget for 1.5oC is exhausted at current (2020) emission levels (around 40 GtCO2)
Warming is defined as the change between current global temperatures (across multiple years) and the baseline temperature level for 1850-1900. Natural variability will lead to warming being more (or less) in some years and locations, but the limits set by the Paris Agreement refer to long-term, global averages. As of 2020, current estimates are that warming has already raised the global temperature by 1.2oC. The Paris Agreement set 1.5oC as the target for maximum warming because of a growing scientific consensus that the impacts and negative risks would grow unacceptably large beyond that level. This assessment is based both on modelling the future and observing the impacts that have already happened due to existing warming. Additionally, the likelihood of irreversible changes is much higher as warming exceeds 1.5oC.
Recent work indicates, with 50% probability, that the remaining carbon budget to not exceed 1.5oC is 440 GtCO2. The amount of uncertainty continues to shrink as we collect more data, better understand the underlying science and build improved models. Yet, there is sufficient uncertainty across all the various variables that even these latest estimates find that there is a small probability that we have no remaining carbon budget. This means that even if emissions were zeroed out today, warming would still exceed 1.5oC.
Implications & Recommendations
At a global level, decision-makers are urged to:
- take immediate and unprecedented actions across all sectors to reduce greenhouse gas emissions, if warming is to stay within 1.5oC above pre-industrial temperatures;
- set both aggressive mid-term goals (e.g. 50% GHG reduction by 2030) and an ambition of net-zero by 2040.
At national and local levels:
- broad and deep electrification utilizing carbon-free sources is a key strategy for decarbonization and sustainable development;
- retirement of economically viable but carbon intensive infrastructure must begin;
- a diverse portfolio of carbon-removal technologies must be rapidly developed and scaled, though not utilized as a replacement for emissions reductions;
- small but immediate reductions in demand can have large impacts on emissions, by enabling the retirement of carbon-intensive energy production (e.g. coal power plants).