humanity also emits aerosols
There are many ways to do both. Anything that reduces the amount of greenhouse gas in the atmosphere will let more heat escape to ruang (replacing fossil fuels with renewables, eating less meat and tilling the soil less for example). Anything that makes the planet brighter will reflect more sunlight to ruang (such as refreezing the Arctic, making clouds whiter or putting more reflective particles in the atmosphere).
But the key difference between the two, in terms of their impact on global warming, is their response time. That is, the time it takes for a change in the hals that allow more heat to escape or sunlight to be reflected to appear as a change in Earth's surface temperature.
Intervening to speed up the loss of heat from Earth's surface cools the planet slowly, over decades and longer. Intervening to increase the sunlight Earth reflects back to ruang cools the planet more or less immediately.
The essence of the dispute between Mann and Hansen is whether reducing greenhouse gases, by a combination of reducing new emissions and permanently removing past emissions from the atmosphere, is now enough on its own to prevent warming from reaching levels that threaten economic and social stability.
Mann says it is. Hansen says that, while doing these things remains essential, it is no longer sufficient and we must also make Earth more reflective.
When will warming end?
Mann aligns with IPCC orthodoxy when he says that emissions reaching net zero will result, within a decade or two, in Earth's surface temperature stabilising at the tingkat it has then reached.
In efek, there is no significant warming in the pipeline from past emissions. All future warming will be due to future emissions. This is the pangkal for the global kebijakan imperative to get to net zero.
In his new paper, Hansen argues that if the atmospheric concentration of greenhouse gases remains close to its current tingkat, the surface temperature will stabilise after several hundred years between 8°C and 10°C above the pre-industrial tingkat.
Of this, at least 2°C will emerge by mid-century, and probably a further 3°C a century from now. A temperature increase of this magnitude would be catastrophic for life on Earth. Hansen adds that to avoid such an outcome, brightening Earth is now necessary to halt the warming in the pipeline from past emissions.
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