In 2004 Stephen Pacala and Robert Socolow sketched a flexible plan for tackling the global warming problem for the next 50 years using only present technologies:
Stephen Pacala and Robert Socolow, Stabilization wedges: solving the climate problem for the next 50 years with current technologies, Science 305 (2004), 968-972.
As they write:
The debate in the current literature about stabilizing atmospheric CO2 at less than a doubling of the preindustrial concentration has led to needless confusion about current options for mitigation. On one side, the Intergovernmental Panel on Climate Change (IPCC) has claimed that “technologies that exist in operation or pilot stage today” are sufficient to follow a less-than-doubling trajectory “over the next hundred years or more”. On the other side, a recent review in Science asserts that the IPCC claim demonstrates “misperceptions of technological readiness” and calls for “revolutionary changes” in mitigation technology, such as fusion, space-based solar electricity, and artificial photosynthesis. We agree that fundamental research is vital to develop the revolutionary mitigation strategies needed in the second half of this century and beyond. But it is important not to become beguiled by the possibility of revolutionary technology. Humanity can solve the carbon and climate problem in the first half of this century simply by scaling up what we already know how to do.
They listed 15 measures, each of which could reduce carbon emissions by 1 billion tons per year by 2054. They claimed that global warming would be manageable, though still a serious problem, if 7 of these measures were carried out by that time. They call these measures stabilization wedges, thanks to their appearance in a chart that illustrates their effects.
In 2011, Socolow said the number of wedges required to hold carbon emissions constant for the next 50 years (i.e., until 2061) had gone up to 9
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