1
00:00:06,800 --> 00:00:09,060
As the sun's rays reach 
the Earth's surface

2
00:00:09,320 --> 00:00:11,590
some are absorbed and re-emitted as heat

3
00:00:11,910 --> 00:00:15,080
greenhouse gases such as water 
vapor and carbon dioxide

4
00:00:15,300 --> 00:00:17,830
absorb and re-radiate some of this heat

5
00:00:18,420 --> 00:00:21,660
increased amounts of greenhouse gases 
in the atmosphere mean more

6
00:00:21,660 --> 00:00:22,500
heat is trapped

7
00:00:22,950 --> 00:00:23,780
warming the Earth

8
00:00:24,510 --> 00:00:25,330
human activities

9
00:00:25,600 --> 00:00:28,490
especially the burning of fossil 
fuels have increased

10
00:00:28,600 --> 00:00:32,160
concentrations of atmospheric 
carbon dioxide by 40%

11
00:00:32,560 --> 00:00:33,940
mainly since 1900

12
00:00:34,540 --> 00:00:38,840
global average surface temperature 
has increased by 0.8° C over that time

13
00:00:40,300 --> 00:00:42,770
Other changes to the climate 
in recent decades,

14
00:00:42,770 --> 00:00:45,050
can be seen in the warming of the oceans.

15
00:00:45,050 --> 00:00:46,230
A rise in sea level

16
00:00:47,010 --> 00:00:49,730
decreasing snow and ice cover 
in the northern hemisphere

17
00:00:50,400 --> 00:00:52,520
and a decline in sea ice in the Arctic.

18
00:00:54,620 --> 00:00:58,480
If emissions continue unchecked 
then further warming of 2.6 to 4.8° C

19
00:00:59,610 --> 00:01:02,880
would be expected by 
the end of the century.

20
00:01:02,880 --> 00:01:04,090
Even at the low end.

21
00:01:04,090 --> 00:01:07,000
This would have serious implications 
for human societies

22
00:01:07,240 --> 00:01:08,240
and the natural world.

23
00:01:12,470 --> 00:01:15,140
For more information about climate 
change from leading science academies,

24
00:01:16,030 --> 00:01:16,670
please visit

25
00:01:16,920 --> 00:01:19,160
royalsociety.org/climatechange

26
00:01:20,160 --> 00:01:23,070
or nas-sites.org/americasclimatechoices