The staggering scale of human CO2 emissions

We've emitted more CO2 than all living biomass and human-made mass combined.

Human activities – burning fossil fuels and cutting down forest – currently emit around 40 billion tons of CO2 per year. But what does that actually mean? How big are our carbon emissions actually?

Comparing our emissions to big things

Forty billion tons (also called gigatons) is an enormous large number. Its about 50 times the weight of all the cars in the world, for example, or the weight of 800,000 Titanic-sized ships.

However, one year’s emissions only tells a small part of the story. We build and sell new cars each year, but the amount of cars on the road is much larger than any individual year’s sales. Similarly, CO2 that we emit accumulates in the atmosphere, such that the amount of warming the world experiences is a result of our cumulative emissions over time rather than a single year’s emissions.

Since the mid-1700s, humans have emitted approximately 2.5 trillion tons of CO2, with around 1,770 billion tons from burning fossil fuels and around 750 billion tons from land use change. About 44% of this – around 1,100 tons – has accumulated in the atmosphere, while the remaining 56% has been absorbed by the land and oceans.

The 2.5 trillion tons of CO2 we have emitted from both fossil fuels and land use change is larger than the total dry living biomass (e.g. all living things on the planet today) and the mass of all human-made structures (all concrete, brick, steel, etc.), as shown in the figure below. If we look at just carbon emissions (keeping in mind that the O2 adds a lot of the mass of CO2), this would translate to around 688 billion tons of carbon.

Cumulative global emissions of CO2 from fossil fuels and land use and atmospheric accumulation from 1750 based on data from the Global Carbon Project. Data on living biomass and human-made mass from Elhacham et al 2020.

The fact that a bit more than half of our emissions are removed by land and ocean “carbon sinks” is a good thing; we would have roughly twice as much climate change to date if we didn’t have these sinks lending us a hand. Unfortunately, the more we emit CO2, the less effective we expect these sinks to become. Under higher emissions scenarios we’d expect more of our emissions to remain in the atmosphere, as shown in the figure below.

IPCC AR6 WG1 Figure SPM.7

Using data on emissions and sinks over time, scientists have created a “global carbon budget” showing where emissions come from and end up. The figure below shows both fossil fuel (grey) and land use (yellow) emissions, as well as ocean (dark blue), land (green), and atmospheric (light blue) sinks.

Global Carbon Budget, 1959-2022. Figure from Carbon Brief’s analysis of the 2022 Global Carbon Budget.

The amount that ends up in the atmosphere accumulates over time, with the sum of all the light blue in this graph representing the total increase in atmospheric CO2 since 1959.

Atmospheric CO2 concentrations from over the past 10,000 years. Figure from Berkeley Earth.

Human emissions of CO2 since the industrial revolution have increased the amount of CO2 in the Earth’s atmosphere by 50%, from 280 to 420 parts per million. This represents a geoengineering of the planet on a staggering scale, and has resulted in the planet warming between 1.1C and 1.3C over the past 170 years.

Global mean surface temperatures from various scientific groups. Figure from the World Meteorological Organization’s State of the Global Climate in 2022 report.