Question

1. Despite large concentrations of CO 2 released by human activity, atmospheric CO 2 is not as high as some would expect. Studies suggest the reason for this is

   	A	addition of new carbon sinks, such as large scale agricultural fields.
   	B	increased evapotranspiration activity by phytoplankton.
   	C	uptake of CO2 by oceans is offsetting atmospheric increases.
   	D	a so-called lag in atmospheric increases in CO2 caused by global circulation.
   	E	international treaties designed to combat atmospheric CO2 releases.

2. General Circulation Models (GCMs)

   	A	are primarily two dimensional models for several weather forecasting.
   	B	offer scenarios of future global warming based on societal choices.
   	C	predict specific future temperatures based on various scenarios.
   	D	can currently only represent atmospheric conditions, though future models will incorporate ocean circulation.
   	E	typically have very fine resolution (e.g., 30 m).

3. How have scientists determined that most of the CO 2 increases have come from human burning of fossil fuels, rather than natural sources?

   A		Prior to the industrial revolution, CO2 concentrations were negligible, while other greenhouses gases dominated the atmosphere.
   B		Paleoclimatological reconstructions which show higher CO2 concentrations than pre-industrial times.
   C		Carbon isotope analysis indicates the source is fossil carbon.
   D		CO2 concentrations are much higher in urban areas than in rural areas, indicating fossil fuels must be the source.
   E		There haven't been enough volcanic eruptions since the observed CO2 increases to account for the additional atmospheric carbon.

Answer 1

A.addition of new carbon sinks, such as large scale agricultural fields

Presence of large scale vegetation fields helps to balance CO2 in atmosphere

A.GCMs are primarily two dimensional models for several weather forecasting.

GCMs are also helpful for understanding the climatic conditions.

A.Prior to the industrial revolution, CO2 concentrations were negligible, while other greenhouse gases dominated the atmosphere.

Burning of fossil fuels causes conversion of organic carbon to CO2, this results high concentration of CO2 in atmosphere.