No one has responded to my question above on the thread, but the following has come to me via an alternative source. Comments on it would be welcome.
The current ecological systems are adapted to live inside the current temperature range. We don't see trees in very hot and relatively dry environments. Most crops won't grow if it gets too hot. A number of crops won't set fruit for example if there arn't enough cold nights. These are just a few examples of consequences of a rapid increase in temperatures. Some areas might indeed become more amenable to agriculture but lack of sufficient daylight (in the norther hemisphere) and poor soils will limit any potential advantage
There is also the likelihood that increases in temperatures will trigger tipping points in various ecological systems around the world releasing huge further amounts of CO2 that would drive temperatures even higher. Particular examples that have been noted are
1) Release of huge amounts of methane currently locked up in the permafrost.
2) Release of carbon in the soil as it gets warmer
3) Reduction of tree cover as higher temperatures destroy current forest areas. This would work in 2 ways. Firstly the dead trees would effectively release further CO2 into the atmosphere. Secondly the (dead) trees would unable to pull CO2 out of the atmosphere
4) Warming oceans would release CO2 back into the atmosphere. The colder the ocean the more CO2 it can hold.
The other issue with a warming world is that extreme heat waves would become far more common. The consequences of this eco systems would be fatal (not to mention us.)
The unfortunate part is that if we believe current scientific research the earth is already committed to at least another 1 degree of warming as result of the CO2 already in the atmosphere . (It just takes a few decades (which is nothing in geological time) for the warming effect to be fully felt. The point of reducing CO2 emissions now is to forstall even bigger temperatures increases.
Apologies for taking so long to respond to this Julia. The question you originally asked was what's so bad about 2 degrees of warming. I'm commenting on the piece you quoted.
It's incomplete and obviously very generalised, but the general direction is right. A global average temperature increase of 2 deg C doesn't just mean slightly warmer breezes. It means more water vapour, which in turn means energy, in the atmosphere, leading to more extreme weather events - droughts, wildfires, cyclones, snowfalls, heavy rains, floods, storm surges, depending on where you are and the season they occur. Extreme weather events are an extra complication in growing food crops, added to changes in pest movements and populations, shifts in germination and pollination periods, loss of certainty for planting times. That all adds up to food shortages, which in turn can be expected to mean rebellions, wars, and increased economic uncertainty.
2 deg of warming also means sea level rise: even if ice sheets in Greenland and Antarctica are not destabilised, the oceans expand as they warm. That leads to higher storm surges, and hence to damage, loss, and possibly abandonment of coastal land and infrastructure.
It's true that there has been rapid climate change in the past and it's probably true that humans and many other species could adapt to climate change in time. However it's also true that the global climate of the last 14,000 years - i.e. the whole of human civilisation - has been stable. Current global average temperature is at or just over (the uncertainty is mine) the top of the range it's occupied for the whole of that time. That means we face a climate of which there is no historical experience at the same time as we face peak oil, peak agriculture, peak fish, peak arable land...
I think the point that fossil carbon emissions to date already commit the earth to further warming is important. The state of the climate in 2020 is to a great extent already determined by past emissions. The urgency now is to prevent greater warming in later decades.
Hope this makes sense. References available in multiple posts from several posters on this thread, or on request.
Ghoti