Where do we stand today ? | whowillcareforme

WHERE DO WE STAND TODAY ?

This section provides you with some very basic answers about the current level of GHG in the atmosphere.

To learn more, you can check the latest 2023 IPCC synthesis report or its 2021 report focusing on the Physical Science Basis and its FAQ

How much did the planet warm up so far?

Since 1850 we cumulatively emitted more than 2500GteqCO2. All those additional emissions increased the concentration of those gases in the atmosphere, thickening the “blanket” keeping Earth warmer. How does this change in the atmosphere chemistry impact Earth temperatures?

The relation between greenhouse gases emissions and an increase of temperatures is simple: for 1000 billion tons of CO2), temperature increases by roughly 0,45°C/ 0.9°F. As we cumulatively added 2500GtCO2 in the atmosphere since 1850, by applying this physical relationship, we found that in theory our planet should have warmed by roughly 1.1°C. This is consistent with what data collected on the ground are showing us. From those data, it has been calculated that our planet is already over 1°C /1.8°F warmer (with a range between 0.8°C/ 1.4°F and 1.3°C) than the pre-industrial era.

Figure 1.12 FROM the IPCC FAQ | Global warming over the instrumental period.

Source: Figure 1.12 in IPCC, 2021: Chapter 1. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Chen, D., M. Rojas, B.H. Samset, K. Cobb, A. Diongue Niang, P. Edwards, S. Emori, S.H. Faria, E. Hawkins, P. Hope, P. Huybrechts, M. Meinshausen, S.K. Mustafa, G.-K. Plattner, and A.-M. Tréguier, 2021: Framing, Context, and Methods. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 147–286,

Worse, it seems that our planet should have warmed up even more if it was not for a counter effect which is happening at the same time. Greenhouse gases are not the only pollutants we send in the atmosphere. Through some of our activities, such as burning coal, we also send other kinds of tiny particles, which are called aerosols. They have a short-term cooling effect on the atmosphere. How so? Those particles once in the atmosphere act like tiny mirrors reflecting the sunlight back into space, thus preventing some of it from being trapped by our greenhouse effect. This cooling effect is assessed to have lowered the temperature between 0°C to up to 0.8°C/ 1.4°F. Without this cooling effect, our temperature would already be over 1.5°C/ 2.7°F. However, those particles are also really bad for human health, especially respiratory heath,that is why we try to get rid of them as fast as we can.

Do we have examples of similar greenhouse gases concentrations in the past?

Looking at the past helps us understand some of the consequences of a higher concentration of greenhouse gases in the atmosphere.

Roughly 3 million years ago, during a period called Pliocene, the atmospheric carbon dioxide concentration was similar to present day. However, the temperatures and sea level were both higher than the ones we are experiencing today (2.5°C to 4°C higher than the pre-industrial baseline (1850-1900) and 5 to 25 m higher when it comes to sea level). How can we explain these differences? The answer is to be found in the inertia of the Earth system. It takes Earth up to centuries to millennia to adjust to a different equilibrium. During the Pliocene the system was fully adjusted. Today we are still at the very beginning of the process: the temperature and sea level have not reached an equilibrium and thus will keep rising.

Does it mean that if we manage to curb our emissions and keep CO2 concentration below a certain level, we will stop temperatures and sea levels from rising right away? The answer is yes and no:

Temperatures are very sensitive to the concentration of greenhouse gas. Once we reach net zero and start pumping CO2 out of the atmosphere, the slowing down of global surface temperature increase would be detectable after about 20 to 30 years.
Sea level rise is not so sensitive as, once triggered by higher temperatures, mechanisms responsible for the rise of sea level (ocean expansion, melting of glaciers and sea caps and ices), cannot easily be put to rest. Due to the massive inertia of the oceans, sea level will keep rising for millenia.

Finally, there is one key difference that prevents the study of the past from helping us fully comprehend what lies ahead: this is the pace at which the concentration of greenhouse gases in the atmosphere is changing. The rate at which we are adding CO2 and other climate pollutants in the atmosphere is 10 times faster than what happened during previous natural climate cycles. In other words, in 100 years we add as much CO2 in the atmosphere as what would happen in 1000 years of natural warming period. As a consequence, we do not really know how ecosystems will cope with such a sharp alteration as it is unique in history, that is why ecosystem collapses are not ruled out by the scientific community. If we are not yet experiencing such dramatic consequences, today we can already see signs of climate change impacting our ecosystems.

FAQ 1.3, Figure 1 FROM the IPCC FAQ| Comparison of past, present and future. Schematic of atmospheric carbon dioxide concentrations, global temperature, and global sea level during previous warm periods as compared to 1850–1900, present-day (2011–2020), and future (2100) climate change scenarios corresponding to low-emissions scenarios (SSP1-2.6; lighter colour bars) and very high-emissions scenarios (SSP5-8.5; darker colour bars).

sources: FAQ 1.3, Figure 1 in IPCC, 2021: Chapter 1. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Chen, D., M. Rojas, B.H. Samset, K. Cobb, A. Diongue Niang, P. Edwards, S. Emori, S.H. Faria, E. Hawkins, P. Hope, P. Huybrechts, M. Meinshausen, S.K. Mustafa, G.-K. Plattner, and A.-M. Tréguier, 2021: Framing, Context, and Methods. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 147–286, doi: 10.1017/9781009157896.003 .]

How much more greenhouse gases can we still pump in the atmosphere if we want to stabilize global temperatures at a +1.5°C/ 2.7°F increase?

As our global temperature already reached an increase of over 1.1°C we can only afford 0.4°C of extra warming to stay below the safest threshold of 1.5°C/ 2.7°F. Going back to our straightforward relationship between CO2 concentration and temperature (for every 1000 GT of CO2 equivalent emitted in the atmosphere, global temperature rises up by 0,45C/0.9F), this means we can only emit up to between 900 GtCO2 and 300 GtCO2, if we want to stabilize temperature at a 1.5°C/ 2.7°F increase.

Why a range and not a single number? That is because there is of course uncertainty in the system (for instance, the starting point of a current 1,1C rise of temperatures is itself the best estimate from a range of temperature increase between 0.95°C to 1.20°C in 2011-2020 compared to 1850-1900). As a result, what the models can predict is a percentage of chances to stay below this 1.5°C/ 2.7°F threshold. Models predict that if we want to increase our chances over 80%, we should only emit 300GtCO2 more in the atmosphere. If we emit 900 GtCO2, our chances drop to a frightening 17% chance to stay below the threshold.

Most of the scenarios that are currently talked through are scenarios where a carbon budget is set at either 420 GtCO2 (which gives us only a 66% chance to stay below 1.5°C), or 580 GtCO2 (our chances dwindle to 50%). In its 2018 report "Global Warming of 1.5°C', the IPCC describes what those carbon budgets look like in terms of emissions pathways:

to get a 66% chance to stay below 1.5°C (with no temperature overshoot) = the 420GtCO2 carbon budget: emissions are halven before 2030 compared to 2010 and net zero emissions is reached in 2040
to get a 50% chance to stay below 1.5°C = the 580GtCO2 carbon budget: emissions are reduced by 45% around 2030 compared to 2010 and reach net zero in 2050.
Other pathways compatible 1.5°C or 2°C allow for a temporary temperature overshoot above which they compensated with a large-scale deployment of carbon dioxide removal measures. Those scenarios are risky and unrealistic as no such technologies currently exist at scale and entail risks.

Furthermore, those carbon budgets can decrease or increase depending on how fast we reduce the other greenhouse gases like methane. Those greenhouse gases need also to follow a drastic reducion pathway.

This analysis should trigger 2 reality checks:

First, we are currently grossly off track to reach a safer 1.5°C target. Under the current actions and policies, we are actually aiming for a World at +3 °C / 5.4 °F by 2100.

Second, the most ambitious reductions pathway currently envisionned by governments (which is the one where emissions are reduced by half around 2030 and reach net zero by 2050) only gives us 1 chance out of 2 to stay below 1.5°C .

To learn more about the concept of carbon budget, you can check the IPCC FAQ 5.4 " What are carbon budgets?"

To learn more about Future Emissions in 1.5°C Pathways and their probabilities to keep us under 1.5°C, you can check chapter 2 of the IPCC Global Warming of 1.5°C.