How fast is warming happening?

Humanity has caused approximately 1.0°C of global warming above pre-industrial levels. Warming may reach 1.5°C as early as 2030 and will continue to rise unless we take quick action. Global warming is happening fast!

So, how fast is warming happening? The United Nations acknowledged climate change in 1996. Since then we have added as much carbon to the atmosphere as in the 146 years from 1850 to 1996.

Greenhouse gases persist in our atmosphere for tens or hundreds of years. The gases already in our atmosphere are effectively locked in, and will contribute to increasing temperatures. In his book “How to Avoid A Climate Disaster”, Bill Gates explains why we need to achieve net zero carbon emissions. He writes “The climate is like a bathtub that is slowly filling with water. Even if we slow the flow to a trickle, the bathtub will still eventually fill up and overflow.“

Even if we stop all emissions today, we cannot avoid some level of warming. The amount of warming we will see, beyond what we have already caused, depends on the changes we make.

So, how fast is warming happening?

In 2018, the IPCC’s “Special Report on the impacts of global warming of 1.5°C“¹ estimated that human activities had caused approximately 1.0°C of global warming above pre-industrial levels. In 2021 the IPCC Sixth Assessment Report (AR6)² reports the world has warmed by 0.8°C to 1.3°C, with a best estimate of 1.07°C. Warming is happening faster than expected.

The figure below shows:

• Panel (a) Changes in global surface temperature reconstructed from paleoclimate archives (solid grey line, years 1–2000). Direct observations are the solid black line (1850–2020). Both both relative to 1850–1900 and decadally averaged. The vertical bar on the left shows the estimated temperature (very likely range) during the warmest multi-century period in at least the last 100,000 years, which occurred around 6,500 years ago during the current interglacial period (Holocene). The Last Interglacial, around 125,000 years ago, is the next most recent candidate for a period of higher temperature. Slow (multi-millennial) orbital variations caused these past warm periods. The grey shading with white diagonal lines shows the very likely ranges for the temperature reconstructions.
• Panel (b) Changes in global surface temperature over the past 170 years (black line) relative to 1850–1900 and annually averaged. This is compared to Coupled Model Intercomparison Project Phase 6 (CMIP6) climate model simulations of the temperature response to both human and natural drivers (brown) and to only natural drivers (solar and volcanic activity, green). Solid coloured lines show the multi-model average, and coloured shades show the very likely range of simulations.

The planet is the warmest it has been for 125,000 years. It is unequivocal that the warming is due to human influence.

What does the future look like?

Global surface temperature will continue to increase until at least mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century – unless deep reductions in CO₂ and other greenhouse gas emissions occur in the coming decades.

The AR6 report considers five emissions scenarios. These predict best estimate global surface temperatures to 2100 as follows.

The last time global surface temperature was sustained above 2.5°C higher than 1850–1900 was over 3 million years ago!

The chart below shows:

• Historical data (thin black line) is observed global surface temperature increase in °C since 1850–1900 as a function of historical cumulative carbon dioxide (CO₂) emissions in GtCO₂ from 1850 to 2019. The grey range with its central line shows a corresponding estimate of the historical human-caused surface warming.
• Coloured areas show the assessed very likely range of global surface temperature projections, and thick coloured central lines show the median estimate as a function of cumulative CO₂ emissions from 2020 until year 2050 for the assessed scenarios for the cumulative CO₂ emissions of each scenario, and each includes the contribution from all anthropogenic forcers.

The most optimistic scenario will see cumulative 2050 CO₂ emissions of nearly 3,000 GtCO₂, while the worst modelled scenario would see cumulative 2050 CO₂ emissions approach 4,500 GtCO₂ emissions.

CO₂ emissions cause most of the warming. Non-CO₂ greenhouse gas emissions cause about a quarter of the warming. See charts below.

Global warming is happening fast. As the caretakers of this planet, only we will determine how warm our Earth will become.  There is still time to save humanity and the world that we know. But we must make choices and implement them quickly.

Ref 1: IPCC, 2018: Summary for Policymakers. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. World Meteorological Organization, Geneva, Switzerland, 32 pp.

Ref 2: IPCC, 2021: Summary for Policymakers. 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.)]. In Press.