How long do we have

How do we know when there is too much greenhouse gases in the atmosphere? Based on the limits suggested by the United Nations, we should aim to cap the increase of temperature to 1.5 °C. It is just half a degree more than we currently have. What’s more, these predictions result from the analysis of the historical data. It can change any time, and not necessarily in our favor. Mother nature is too complex to predict it solely from her past behavior. Scientist discover that they constantly need to adjust their models.

To estimate how much time we have left before it’s too late, scientists use Carbon Dioxide Equivalent concentration. They sum all the greenhouse gases in the atmosphere based on their Global Warming Potential (GWP) and express it in CO2 equivalents. It’s as if we only had CO2 from all the greenhouse gases sitting in the atmosphere.

Based on the chart below, the cumulative presence of greenhouse gases in the atmosphere over time, expressed in CO2 equivalents is contrasted with the temperature increase corresponding to them. Predictions of the levels of CO2 equivalents triggering 1.5 °C increase and 2 °C are shown as the dotted lines. Extrapolation is then made to see how long do we have. You can see how close we are already.

Observed concentrations of all greenhouse gases (including aerosols) between 1970-2017

The chart shows the data until 2016, however, the report based on this data was published at the end of 1st quarter 2019. Researchers concluded that to keep the rise of the temperature below 1.5 °C we can’t let the concentration to increase to more than 478 PPM of CO2 equivalents and to 545 PPM if we are to stay below 2 °C increase. These numbers show a 50% probability, which means that even at these levels, the chances to remain below the cap and exceed it are equal (nature is unpredictable).

So what’s with the timing? Experts predict that we can reach 1.5 °C mark in 5-16 years from 2019, and 2°C mark in 17-40 years if the current rate persists. It is estimated that in 2016, carbon dioxide alone was responsible for 66.2% of the increase of the warming (forcing), followed by 17% contribution by methane and 8.9% of Montreal Gases (the ones depleting the ozone layer, more on them later). The conclusion for us is to focus on reducing these gases emission in the atmosphere first of all, with special attention given to carbon dioxide.

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