In 2015, the annual mean global atmospheric carbon dioxide (CO2) level surpassed 400 parts per million (ppm; Figure 1.1), and we know very well that this rise is caused by human activities (Figure 1.2). It was the first time in 3 million years that such a level had been reached. Crossing this level has caused widespread concern among climate scientists, and not least among those called pale climatologists, who work on natural climate variability in prehistoric times, before humans. Over the last few decades, researchers have been repeatedly raising the alarm that emissions of CO2, along with those of other greenhouse gases, are getting dangerously out of control and that urgent remedial action is needed. With the crossing of the 400 ppm threshold, this sense of urgency reached a climax: at the Conference of Parties 21 meeting in Paris—also known as COP21 or the 2015 Paris Climate Conference—broad interna¬tional political agreement was reached to limit global warming to a maximum of 2°C, and if at all possible 1.5° C, by the end of this century. If one calculates this through, this implies a commitment for society to operate on zero net carbon emissions well before 2050, along with development and large-scale application of methods for CO2 removal from the climate system. (Scientists focus on carbon (C) emissions when they discuss emissions because it helps in calculating CO2 changes produced by the processing of specific volumes/ masses of fossil fuel hydrocarbons.) Clearly, the challenge is enormous, especially given that even implementing all the pledges made since COP21 would still allow warming to reach about 3°C by 2100. But, regardless, the agreement was ground breaking. It was a marker of hope, optimism, and international motivation to tackle climate change. Moreover, there are concerns about the stated COP21 targets. First, the proposed 2°C or 1.5°C limits to avoid 2 “dangerous” climate impacts may sound good, but there is no specific scientific basis for picking these particular numbers. Second, the implied “end of this century” deadline is an arbitrary moment in time.
Liquid amine–solid carbamic acid phase-separation system for direct capture of CO2 from air