[kakapo88]

You're not considering timescales. True, the earth has seen all sorts of climates .. over slow-moving gradual timeframes of 100k to millions of years. And in none of those situations did human civilization exist - relying on specific climatic conditions for food, water and so on.

But now, climate is changing 1000x as fast. And we have civilization of 8 billion people, many of them living on the margins in areas that will soon became less habitable.

So you don't need Venus. Just a few degrees means hundreds of millions of refugees, food shortages, water shortages, and no doubt mass conflict as a result.

Don't confuse geologic time with human time.

[crypot]

A 2c rise in temperature is insignificant compared to seasonal variation. There is no evidence that this change would decrease biodiversity on earth. All the evidence points the other way.

Climate change will be a humanitarian issue. People claiming that it will lead to ecosystem collapse and a loss of biodiversity are just a distraction. They are taking time and resources away from the real issues.

A warmer planet will have more biodiversity, not less. It will be easier to support 8 billion humans with a warmer, more productive planet.