System inertia :
What is terrible with the problem of global warming, is inertia of what has been triggered.
Even if we stop now to emit CO2, the mechanism started will continue over hundreds of years. Because CO2 remains an average of 120 years in the atmosphere, and CH4 remains an average of 20 years.
And as human emissions of greenhouse gases are not near to stop, or even decrease, or even simply not to increase. So the worst is sure.
Limiting the increase to +2°C in 2100 is a utopia.
Moreover this figure of +2°C which is presented as an ambitious goal will not be respected.
Many civilizations have disappeared, but they did not have the level of understanding of their environment sufficient to analyze their decline and anticipate needed actions.
Whether it be on historical plans, economical, political, ecological, etc, these civilizations did not understand problems and disappeared.
We are probably the first civilization able to understand why and how we will have big problems, and moreover we see it well in advance.
But more likely is that despite the fact that we know, we will not act, and we will do as civilizations that have preceded us.
It's like a young smoker who knows that lung cancer will happen in the few decades, but which will continue its harmful practice, to death.
The paradox of fossil fuels : coal, then oil and gas have enabled the industrial revolution and current level of life, but produced greenhouse gases emissions will generate the decline of civilization.
Moreover carbon sinks are becoming less efficient.
Arctic regions are warming faster than other areas (albedo problem).
So, Svalbard, Greenland, Alaska, risk to see their ice to melt faster.
The emitted CO2 stock will not decrease quickly (120 years of lifetime).
These vicious circles are doing that we are going towards something very bad.
Even if the global temperature increase would remain below 2°C, increase in sea level will be important.
+2°C is an objective. An objective, not a reality. This objective will be exceeded, and probably widely.
There is a system runaway, for example, with the release of methane after permafrost melting.
Oceans temperature is only at the beginning of his rise, because there is an enormous inertia. So there is a great potential for expansion.
The IPCC does a remarkable scientific work. But the caution inherent to scientists tend to make that they minimize consequences, or to propose a range of options ranging from low to high.
Their work is the opposite of tabloids's sensationalism. But we have to anticipate future problems, if we do not want to suffer them.
So we must consider high estimates.
Moreover, more studies are progressing, more we are seeing bad news, feedbacks amplifying phenomena.
Usually in nature, retrofeedbacks allow to achieve a balance.
But in the case of climate changes, it's the opposite.
For example, carbon sinks work much less well (oceans, soil, plants, etc), and in some cases, carbon sinks become even carbon emitters.
For the glaciers melting, phenomena such as subglacial water runoff, surface melting, etc, are very worrying.
A very high hypothesis is possible (probable ?) :
- there are not much efforts to limit anthropogenic greenhouse gas emissions,
- temperature rises,
- permafrost melting causes more CH4 and CO2 release,
- there are strong methane hydrate releases.
In this case, sea level rise will be very problematic.
We will see effects of massive CO2 emissions.
Climate change is a real scientific experiment on the planet scale.
The bad news is : in this scientific experiment we are the guinea pigs.
So, those who will suffer the consequences, that's us. It's annoying.
If we have a massive release of methane from methane hydrates, in this case . . .