Man-Made Climate Change
There is a substantial body of research that details anthropogenic, or man-made, climate change. Climate mitigation policies have largely been based on the evidence that has resulted in this scientific consensus. In particular, the Paris Climate Agreement, which was finalized in 2015 and opened for signatures in 2016, is perhaps the most comprehensive of these policies.
The historic agreement, which has been signed by 143 of the 197 total participating nations, aims to reduce the presence of carbon dioxide (CO2) and other greenhouse gases in the atmosphere. Concretely, it sets a goal of limiting global average temperature increase to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels and of pursuing efforts to limit temperature increase even further to 1.5 degrees Celsius (2.7 degrees Fahrenheit).
However, how these goals are to be achieved have largely been left on the discretion of the individual countries. This is where a new study published by the International Institute for Applied Systems Analysis (IIASA) in the journal Nature Communications comes in.
A Plan for Change
The IIASA researchers, led by World Bank consultant Brian Walsh, used a global model of the carbon system which monitors both natural and anthropogenic activities that account for carbon uptake and release. “This study gives a broad accounting of the carbon dioxide in our atmosphere, where it comes from, and where it goes” Walsh explained in an interview for a IIASA press release. "We take into account not just emissions from fossil fuels, but also agriculture, land use, food production, bioenergy, and carbon uptake by natural ecosystems.”
The findings showed that, for the Paris Climate Agreement's goals to be realized, global energy supply must only be 25 percent dependent on fossil fuels by 2100. However, simply limiting greenhouse gas emissions is not enough. In addition, carbon sinks, like forests, must be preserved so they can continue to absorb carbon. The researchers found that land use must change in order to reduce cumulative emissions to 45 percent by end of the century.
If nations can work together to attack climate change by both reducing fossil fuel consumption and by enforcing environmentally friendly land use, we could reach zero net anthropogenic emissions well before 2040. This could allow us to achieve the goal of 1.5 degrees Celsius (2.7 degrees Fahrenheit) by 2100, according to coauthor Michael Obersteiner, Ecosystems Services and Management Program Director at the IIASA.
The model of a "high renewable" future for energy showed an ambitious but possible alternative. In this scenario, a yearly 5 percent increase in renewable energy dependence could lead to a peak in net carbon emissions by 2022. It's an entirely plausible scenario, especially since renewable energy consumption has been on the rise. However, renewables have to be combined with negative emissions technologies, for without these global average temperature could still rise to 2.5°C — missing the Paris Climate Agreement's goals.