1.9 What are greenhouse gas emissions like today?
"More than half of all industrial emissions of carbon dioxide since the dawn of the Industrial Revolution will have been released since 1988"
Dr. Peter C. Frumhoff, Director of science and policy at the Union of Concerned Scientists
Due to a deadly combination of burning fossil fuels and changes in land use, we are currently pumping out a whopping great 110 million tonnes of carbon dioxide into the atmosphere every 24 hours. That’s over 40 billion tonnes a year! Over the past 60 years, the annual rate of increase in atmospheric carbon dioxide has been about 100 times faster than any previous natural increase in at least the last 800,000 years, such as those that occurred at the end of the last ice age around 12,000 years ago - see graph in section on how natural fluctuations in carbon dioxide have affected the Earth’s temperature.
The scary thing is that because carbon dioxide stays in the atmosphere for such a long time, even if we completely stopped emitting it today we would not reverse the warming that it has caused. It’s like [filling a bathtub with the plug in it] (https://www.skepticalscience.com/SkS_Analogy_10_Budgets_and_Bathtubs_V2.html): the water level will keep going up as long as the tap is on, but once you turn the tap off it won’t go down unless you remove water from the tub. Likewise the level of carbon dioxide and the heating it causes depends on the total amount of carbon dioxide emitted over time, and temperatures will not go back down even once we stop emitting carbon dioxide. If we want to reduce global temperatures, we will have to actively remove carbon dioxide from the atmosphere, something which might be impossible to do at the scale required.
This means that the only way we can definitely avoid catastrophic and irreversible damage to our planet is if we reduce carbon dioxide emissions to zero before we reach the level of heating that would cause such changes. This leads to the concept of a "carbon budget" - the maximum amount of carbon dioxide we can emit over the whole century if we want to stay below a certain temperature.
The picture is slightly better for the shorter-lived greenhouse gases, such as methane. Just like how in an unplugged bathtub the water level will drop as soon as the tap is turned off, if we stopped emitting methane today, the amount that it heats the atmosphere would drop almost immediately. This makes reducing methane emissions a very effective way to slow the rate of global heating.
However, there is much more carbon dioxide in the air than other greenhouse gases and it stays in the atmosphere for longer, so reducing carbon dioxide emissions is still the most important factor in determining how much the Earth heats up overall/. So if we want to keep the global temperature rise to below 1.5°C, it is essential that we rapidly reduce global emissions of both short- and long-lived greenhouse gases.
Yet despite all the policies and pledges from the government, global greenhouse gas emissions continue to shoot up at an alarming rate. Whilst there has been a recent drop in emissions due to the COVID-19 pandemic, the short term effects on climate will be minimal, and unless concerted effort is taken to stop fossil fuel development in the recovery period it will only be a temporary dip in a long-term upward trend. If this is a hole we need to get out of, we’re still digging.
Indeed, Fatih Birol, executive director of the International Energy Agency and one of the world’s foremost energy experts has warned that we have to act quickly if we want to change the course of the climate crisis and prevent a post-lockdown rebound in greenhouse gas emissions that would overwhelm efforts to stave off climate catastrophe. Birol said: "This year is the last time we have, if we are not to see a carbon rebound."