2 
00:00:05,857 --> 00:00:12,680 
We can't see or taste CO2. 

3 
00:00:12,680 --> 00:00:15,450 
The thing that really bothers us is the 
temperature. 

4 
00:00:15,450 --> 00:00:21,190 
A natural evolution of this was to 
graduate to temperature targets. 

5 
00:00:21,190 --> 00:00:26,620 
What does it take to keep earth's 
temperature at some given level? 

6 
00:00:26,620 --> 00:00:31,680 
some kind of a benchmark? 
The European Union has taken 2 degrees C

7 
00:00:31,680 --> 00:00:36,160 
as a target 
temperature change. 

8 
00:00:36,160 --> 00:00:40,970 
Two degrees C is warmer than the earth 
has been in millions of years. 

9 
00:00:40,970 --> 00:00:44,730 
It's warmer than it has been the whole 
time that 

10 
00:00:44,730 --> 00:00:49,160 
civilized humanity has existed, with 
agriculture,

11 
00:00:50,756 --> 00:00:57,225 
so a more conservative temperature target 
is advocated by Jim Hanson. 

12 
00:00:57,225 --> 00:01:00,270 
One degree C is within the natural 

13 
00:01:00,270 --> 00:01:05,020 
range of climate variability
throughout the

14 
00:01:05,020 --> 00:01:06,910 
period of time covered by the 

15 
00:01:06,910 --> 00:01:10,450 
ice cores, the last hundreds of 
thousands of years. 

16 
00:01:10,450 --> 00:01:16,300 
And if we could keep Earth to within one 
degree C, it decreases 

17 
00:01:16,300 --> 00:01:22,960 
the odds of provoking some kind of a slow 
Earth system feedback. 

18 
00:01:22,960 --> 00:01:25,520 
Like the collapse of ice sheets,

19 
00:01:25,520 --> 00:01:29,290 
the release of extra carbon from melting 
permafrost,

20 
00:01:29,290 --> 00:01:33,860 
and methane hydrates in the ocean, changes 
in ocean chemistry. 

21 
00:01:33,860 --> 00:01:37,052 
All kinds of scary things that are 

22 
00:01:37,052 --> 00:01:40,748 
outside what's happened in the 
last half 

23 
00:01:40,748 --> 00:01:43,604 
a million years, we could avoid if we could 

24 
00:01:43,604 --> 00:01:47,220 
keep the temperature to one degree C or 
less.