Uncommon truths: Raising the temperature
2024 could be the hottest year on record. There may be some temporary factors but the trend looks set for a 3-40C change by 2100. This suggests we need massive mitigation and adaptation spending.
Summer seemed to arrive late in Europe, except in the extreme North and South, and was often punctuated by heavy rain (witness the opening ceremony of the Paris Olympics). Hence, it is hard for us to believe that global temperatures have been hitting record highs, but they have. It seems quite likely that 2024 will be the hottest year on record (2023 was the previous high). We think this is due partly to the effect of El Nino conditions in the Pacific Ocean but also to the ongoing effects of greenhouse gas emissions. The former may reverse with the transition to La Nina conditions but we expect past, current and future emissions to continue raising temperatures beyond of the end of this century.
According to the European Union’s Copernicus Climate Change Service, the global average surface air temperature for July was 16.910C. That was marginally below the 16.950C recorded in July 2023 (the hottest July on record), thus ending a 13-month run when each month was the warmest on record for that month of the year. Even though July was not the warmest ever, it contained the two hottest days on record (17.160C and 17.150C on 22 July and 23 July, respectively). The January-July global average temperature is 0.270C above the same period of 2023, so it is possible that 2024 will be the hottest year on record (even allowing for the expected transition from warming El Nino to cooling La Nina conditions).
As for the Paris Agreement’s aim to limit the rise in temperature since 1850-1900 to 1.50C, the global temperature in July was 1.480C above the 1850-1900 average for July (the previous 12 months had all exceeded the 1850-1900 average by at least 1.50C).
Perhaps contributing to those record air temperatures are elevated sea surface temperatures (SST), which had been at record seasonal levels since April 2023. July was the first month since then that SST didn’t set a record for the month. The 20.880C in July 2024 was marginally below the year earlier July record of 20.890C (based on global averages in 600S-600N latitudes).
Are rising temperatures (and broader climate change) caused by human activity? Perhaps it is just coincidence, but the atmospheric concentration of CO2 reached a new high of 421.08 parts per million (ppm) in 2023, according to data from the US National Oceanic and Atmospheric Administration. Figure 1 shows this to be well above the norms of the last 800,000 years. As CO2 concentration appears to be correlated to CO2 emissions in the previous one hundred years (according to our analysis), it seems likely that rising CO2 emissions may have contributed to rising temperatures (molecules of greenhouse gases such as CO2 absorb energy, thus holding heat in the atmosphere that would otherwise have escaped).
Note: “Actual” data is from the year -803,719 (i.e. 803,719 B.C.) to 2024. Data is not available for all years, so the date axis is not to scale. Data is shown for each year from 1750, using simple interpolation to fill any gaps. Data from 1958 to 2023 is based on observations at the US National Oceanic and Atmospheric Administration’s (NOAA) Mauna Lao Observatory on Hawaii. The 2024 datapoint (423.9 ppm) is based on the forecast change for 2024 produced by the UK’s Meteorological Office. Data prior to 1958 is derived from ice core records, as provided by NOAA Earth System Research Laboratories. Projections assume that CO2 concentration is determined by emissions in the previous 100 years (using an econometric relationship derived from data since 1750). Projections rely on forecasts of future CO2 emissions by low, middle and high-income countries (the global total being an aggregation of the three): “recent trends” assumes a continuation of recent trends in declines in the CO2 intensity of GDP and growth in GDP per capita, whereas “optimistic” assumes a more aggressive reduction in CO2 intensity (see the detailed explanation in the appendix). In both cases, population forecasts are taken from the UN’s World Population Prospects 2024. “Industrial revolution” is the period 1760-1840. Source: NOAA, Our World in Data, UK Meteorological Office, United Nations, World Bank, LSEG Datastream and Invesco Global Market Strategy Office
The good news is that we can do something about it (if we are responsible). However, CO2 emissions hit a new high in 2023 (40.4bn tonnes, according to the Energy Institute Statistical Review of World Energy). I reckon they will continue climbing, using a model that calculates CO2 emissions as the product of population, GDP per capita and the CO2 intensity of GDP.
Of course, the outcome depends on the assumptions. UN Medium Variant projections suggest the world’s population will rise from 8.09bn in 2023 to a peak of 10.29bn in 2084. Luckily, that peak is around 1bn lower than predicted in 2015 (total population was then expected to reach 11.21bn in 2100 and to go higher). Nevertheless, if real incomes (and spending) continue to rise, that 27% gain in population will require massive technological shifts to stabilise CO2 emissions. Figure 2a shows that we are on the right path, with a gradual decline in the CO2 intensity of economic activity. Technological change will hopefully drive it even lower.
Unfortunately, it isn’t happening fast enough. If CO2 intensity follows recent trends, I estimate that annual CO2 emissions will almost double by the time they peak in 2073 (assumptions are in the appendix). Based on my models, this, and the emissions of recent decades, will result in a further rise in the atmospheric concentration of CO2 (see “Projected (recent trends)” in Figure 1). This leads me to conclude that by 2100 the global temperature will be 4.00C higher than the 1850-1900 average, based on the model shown in Figure 2b (it shows the variance versus 1961-1990).
A highly optimistic scenario, that sees high income country gross emissions fall to zero by 2060 and a doubling of the rate of decline in CO2 intensity in low and middle income countries, gives the result that global CO2 emissions fall from here and would halve by 2087 (and be almost zero by the end of the century). CO2 concentration would continue to climb because of emissions over recent decades (see “Projected (optimistic)” in Figure 1), but would peak in 2084. Nevertheless, I still predict a temperature gain of 3.20C versus 1850-1900 by the end of the century, which shows the scale of the challenge facing us.
Even on my most optimistic scenario (accepting the simplicity of my models), the temperature change outcomes would be dramatic, as would the potential implications for volatile weather patterns, rising sea levels, agricultural production and migration flows. The 2100 temperature projections are roughly 0.25C higher than what was suggested just three years ago, which shows how little progress we are making (even allowing for the recent El Nino effects to fade). The world may need big investment in carbon reducing and carbon removing technology, running the gamut from reforestation, through electrification of transport systems to renewable energy sources (as previously covered in The 21st Century Portfolio, November 2019, and in recent editions of Economic Transition Monitor). In the meantime, large scale adaptation spending may be needed as we learn to live in a changing world.
Unless stated otherwise, all data as of 30 August 2024.
Notes: Figure 2a shows the CO2 intensity of GDP annually from 1990 to 2023 for low, middle and high-income countries (as currently defined by the World Bank). Figure 2b shows annual data from 1850 to 2100. It shows the historical global temperature variance (“Temp variance”), which is the global average land-sea temperature anomaly relative to the 1961-1990 average temperature in degrees Celsius, median estimate, as provided by UK Met Office Hadley Centre. “Fitted temp variance” is the result of a regression analysis that fits historical temperature variance to atmospheric CO2 concentration (using the natural logarithm of the 100-year moving average of concentration, on the assumption that temperature at any moment is determined by CO2 concentration during the previous 100 years). “Predicted (recent trends)” applies that fitted relationship to our forecast of CO2 concentrations, assuming that recent trends in CO2 intensity and GDP per capita continue, though with some convergence between World Bank income groups after 2050 (see appendix for details). “Predicted (optimistic)” assumes a doubling of the rate of decline in CO2 intensity (with the added assumption that high income CO2 emissions trend to zero in 2060). Source: NOAA, Our World in Data, UK Meteorological Office, United Nations, World Bank, LSEG Datastream and Invesco Global Market Strategy Office
