Climate and energy data is often presented in units that may be unfamiliar. But the units chosen here are intended to make comparisons simple. So, it is more important to notice, for example, that since the year 2000 the EU decreased its annual greenhouse gas emissions from 4 Gt to 3 Gt than it is to know what a “Gt” is, but a full explanation of these units follows at the end of this section.

Humans emit about 40 Gt (gigatons) of CO₂ each year. Activities like clearing forests and making cement also increase CO₂ levels, and certain other activities produce additional greenhouse gases, such as methane, that add the equivalent of another 10 Gt of CO₂ emissions.

Half of CO₂ emissions are absorbed by vegetation and the oceans. But much of the CO₂ absorbed by the oceans becomes dissolved carbolic acid, which is changing the chemistry of seawater and destroying marine life.

Sea levels are rising about 4 cm (1.5 inches) every ten years because of the enormous quantities of water from the melting of glaciers and polar ice caps as well as from the expansion of the sea water as it warms.

Of course, greenhouse gas emissions produce other negative effects as well, such as drought and extreme weather. And all of these changes are speeding up.

In 2021 the world consumed 168 PWh (Petawatt-hours) of energy. Most of this energy came from fossil fuels; only about 16% came from low-carbon sources.

All fossil fuels add CO₂ to the atmosphere. Coal releases the most. Very roughly. burning various types of oil produces about 75% as much CO₂ as coal for the same amount of energy, while natural gas releases a little over 50% as much.

To approach the goal of net zero greenhouse gas emissions by 2050, that 16% of energy from low-carbon sources must climb to very nearly 100%.

Half of CO₂ emissions are absorbed by vegetation and the oceans. But much of the CO₂ absorbed by the oceans becomes dissolved carbolic acid, which is changing the chemistry of seawater and destroying marine life.

Between 2000 and 2024, global energy demand increased by an astonishing 93%. Of that consumption, 38% could be attributed to renewable sources and 8% from nuclear. However, the remaining 54% still comes from fossil fuels. While energy from wind and solar has increased rapidly since 2000, total low-carbon energy has increased more slowly because the share of total energy from nuclear power has decreased.

Many people consider nuclear energy to be controversial, but nuclear energy produces very little carbon and is among our cleanest energy sources. Unfortunately for the climate, many of the new sustainable energy sources replaced nuclear energy rather than fossil fuels.

Western industrial nations have been gradually decreasing their greenhouse gas emissions since 2000. But during the same period developing regions, especially China, have greatly increased their coal consumption and greenhouse gas emissions, more than offsetting the modest reductions in the West.

But as we will see, these numbers are not as simple as they might at first appear. The reports that follow examine more closely the energy use, greenhouse gas emissions, and plans for developing low-carbon energy in major consuming regions.