I'm going to give you this.

Okay

How much will climate change cost if we do nothing now?

Well, the answer to that, in some sense, is we don't know.

But, last year the Intergovernmental Panel

on Climate Change put out a report

where it estimated that if nothing was done

and if warming increased to 1.5 degrees Celsius

- bearing in mind we've already had about one degree of warming

- the global cost of climate change damages

is likely to be around $54tn by the end of the century.

If we reach 2 degrees of warming,

their estimate is that by the end of the century

we could be looking at $69tn worth of damage.

But there's a lot more to costs than just economics.

There's the survival of life, some of which

we are dependent upon.

Two degrees is too warm for most of the coral in the oceans.

About 99 per cent of corals would be gone.

Changes to ocean temperature and ocean acidification

would also mean that the global catch of fisheries

would be about half of what it is at 2 degrees.

So focusing on the costs in narrow economic terms

for a transformation of this scale and irreversibility just

seems inappropriate.

Sea level rises are important.

Desertification, the expansion of deserts

and the shift of rainfall patterns across the globe,

could be immensely important in affecting humans' ability

to carry out agriculture, indeed to survive.

We could also see intensified conflict, migration.

The combination of extreme weather and higher seas

is going to make living near the coast much riskier.

And many of the changes that climate change will bring

are really going to stress governance systems.

Their big message is if we can hold global warming

to 1.5 rather than 2 degrees, we'll

be a whole lot better off.

The trouble is, in order to avoid 1.5 degrees of warming,

we need to halve emissions from what they are now by 2030,

and then we need to bring them down to around net zero, almost

nothing, by 2050.

That's incredibly difficult. No other generation

has done this before.

So the sensible way of thinking about this

is there are huge irreversible risks here.

They will have economic and many other costs.

And if we're sensible, we don't want to run these risks.