The Environment: carbon dioxide emissions

To start with, let's try to frame the problem.

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56.6% of total greenhouse gas emissions are CO2 emissions created by burning fossil fuels (IPCC, AR4, Figure 1.1b). According to the US Carbon Dioxide Information Analysis Center, total world CO2 emissions in 2006 were 8230 million metric tons. This subdivides by type into 1521 mmt (million metric tons) from gaseous fuels, 3108 mmt from liquid fuels, 3193 mmt from solid fuels and some 400 mmt from cement production and gas flaring.

The IPCC's Working Group III, Assesment Report 4 (link):

The largest growth in CO2 emissions has come from the power generation and road transport sectors, with the industry, households and the service sector remaining at approximately the same levels between 1970 and 2004 (Figure 1.2). By 2004, CO2 emissions from power generation represented over 27% of the total anthropogenic CO2 emissions and the power sector was by far its most important source. Following the sectoral breakdown adopted in this report (Chapters 4–10), in 2004 about 26% of GHG emissions were derived from energy supply (electricity and heat generation), about 19% from industry, 14% from agriculture, 17% from land use and land-use change, 13% from transport, 8% from the residential, commercial and
service sectors and 3% from waste (see Figure 1.3).
[IPCC III, AR4, 1.3.1]

Sources of direct global CO2 emissions in 2004 were as follows [IPCC III,AR4,1.3.1], in GT CO2/year:

Electricity plants: ~10 GT
Industry (excluding cement production): ~5 GT
Road transport: ~4.5 GT
Residential and service sectors: ~4 GT
Deforestation: ~3 GT
Other: ~2 GT*
Refineries etc. ~2 GT
International transport (incl. aviation and marine tpt): ~0.5 GT

(*: "Other domestic surface transport, non-energetic use of fuels, cement production and venting/flaring of gas from oil production)

10% of the emissions counted as deforestation are from burning wood as fuel.

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So in short, the most significant source of CO2 emissions is electricity generation, closely followed by industry and road transport. It's worth noting that that bugbear of the environmental movement, air travel, is way down on the list.

This strongly suggests, at least in my opinion, that any policy aiming at reducing CO2 emissions would need to focus on these areas.