Greenhouse gases (GHG) act as a blanket increasing the temperature on the surface of the Earth. This is a natural phenomenon however due to man-made carbon pollution; the global climate is changing much faster than animals and plants can adapt. How human society will adapt is still an open question.
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There are many different GHGs. The most common is carbon dioxide (CO2). To make calculations easier we normalize all GHG numbers to carbon dioxide equivalent (CO2eq). For example, 1 ton of methane has the same warming effect as about 80 tons of CO2, so we normalize it to 80 tons CO2eq. We may shorten even further to just carbon, which is a term often used to refer to all GHGs.
The goal set by the UN IPCC and agreed and ratified by 195 states in the Paris Climate Agreement is to reduce carbon pollution so that the temperature increase stabilises to a 1.5 °C increase by 2100.
The temperature increase on the Earth is dependent on the total amount of carbon we have in the atmosphere, not the rate at which we are emitting. To completely halt the rate of temperature increase, we need to stop adding carbon to the atmosphere or achieve net-zero emissions.
Net-zero means for each gram of carbon we emit we also extract 1 gram, so the overall mass of carbon in the atmosphere remains fixed.
In order to achieve this, we need to mobilize as a global community. We need to start immediately reducing our carbon emissions with the goal of a 45% reduction by 2030 and to reach net-zero by 2050.
To be carbon efficient is to minimize the amount of carbon emitted per unit of work.