Environmental Engineering Reference
In-Depth Information
underpin the level of concern, strengthen commitment to targets for emission
reductions and heighten expectations of impacts and adaptive needs.
Key Challenge: to provide greater guidance as to the definition of 'dangerous'
climate change.
Additionally, there are strategic challenges in developing the underpin-
ning science that need to be addressed. These include:
•
determining the likelihood that the net uptake of carbon by the
global biosphere (which has characterised the global carbon budget
of the last two decades) will reverse to become a source of carbon
dioxide leading to a greater growth rate of carbon dioxide in the
atmosphere
•
determining the risk of the thermohaline ocean circulation slowing
in the next few decades, which would impact on the rate of oceanic
uptake of carbon dioxide and thus the rate of future climate change
•
determining the likelihood that warming rates per unit of
concentration increase may currently appear slower than they might
be in the future, due to the 20th century growth in aerosol emissions
(which may have a cooling effect) masking of some of the greenhouse
warming.
Challenge: to provide sound understanding upon which the risk of climate
change can be assessed, including the impact of changes in net carbon uptake
by the global biosphere, potential slowing of thermohaline ocean circulation,
and the masking effects of aerosol emissions.
Challenges for emission reduction and energy systems
The IPCC key message that human influence will continue to change climate
throughout the 21st
century arose out of a huge research effort related to the
global biogeochemical cycling of carbon dioxide between the atmosphere,
oceans and terrestrial ecosystems. The carbon dioxide cycle is now reasona-
bly well understood - enough to know that when a molecule of carbon
dioxide is released into the atmosphere, it effectively resides there for almost
100 years. The very important message arising out of this finding is that
slowing the growth of emissions of carbon dioxide into the atmosphere will
