1. You can make up your
own vertical scale - could be in terms of sea level, number of species
remaining, human mortality rate etc. I believe human mortality related to global warming
is currently around 300,000 per year, but wars instigated by resource shortages and
land degradation can have a big effect on this number.
2. If there are no significant behavioural or technological
changes (black line), and the enhanced global warming trend continues, the
future is unpredictable because the earth's behaviour cannot be modelled in this region.
3. If there are technology developments which could
help sustain the environment, but they are not widely taken up, they will have little
effect - hence the plummeting blue line.
4. My favourite line is the red one - preferably voluntary (worldwide)
behavioural changes with technology advances. I've been optimistic
and shown an improving situation in time but we can't recreate non-renewable resources
and extinct species, and re-freezing ice caps or removing excessive greenhouse gases
from the atmosphere could be tricky ....