Is it better for the environment to cook with gas or with electricity, assuming the electricity does not exclusively come from renewable sources? I am interested in a comparison for each of the following categories:
It's going to depend on several factors. There is no one universal answer. It will depend on:
So it's not possible to give a specific answer, with regard to your three criteria. For the specifics of your own case, you'd need to look at lifecycle assessments (LCA) for each of the energy vectors. But let's look at some generalities:
If your electricity supply is not preominantly coal, and you've got efficient electrical cooking (e.g. induction hob, microwave oven, well-insulated convection oven), then cooking with electricity is likely to be better.
It's also likely that your electricity supply will get cleaner over the next 10 years, i.e. within the lifetime of any cooking device that you buy now, so the balance may tip towards electric within the lifetime of a cooker bought today.
If:
then cooking with gas is likely to be better.
If your electricity is mostly coal, and your gas supply is as leaky as many seem to be, then cooking is going to be quite carbon-intensive either way; that is, there will be high greenhouse gas emissions per unit of energy that actually gets delivered into cooking. In that case, the best option to take you closer to sustainability is find an energy provider who can supply you with cleaner electricity or gas.
Cooking tends to be a pretty small part of overall energy consumption (a tiny few percent), so the overall environmental impact from cooking is likely to be a very small part of your total impact.
Here#s a quick outline on some relevant efficiencies. The reciprocal of the overall efficiency is the multiplier for environmental damage: for example, an overall efficiency of 33% means that 1 unit of energy used directly for cooking does 3x the damage: An overall efficiency of 50% means 2x the damage. 25% means 4x the damage. etc.
Remember that methane has a global warming forcing of about 21-25, relative to CO2, at the 100-year time horizon, so methane leakages are significant contributors to climate damage.
Your phrase "not exclusively from renewable sources" straddles a great deal of ground, which makes any answer necessarily hedged. Great job above by EnergyNumbers. If I might illustrate my point: Look at BC Canada vs. California USA.
http://www.empr.gov.bc.ca/EPD/Electricity/supply/Pages/default.aspx
^^ Those are just estimates, but 82% hydroelectric and 10% biomass, with only 5.6% natural gas, tells me you (if in BC) should be using electricity wherever possible.
http://www.getenergyactive.org/fuel/state.htm
Whereas California is clearly a different situation, with 17% hydroelectric and 14% other renewable sources, and natural gas at 52% of the supply. California is clearly trying, and will improve, but it's not hard to conclude a Californian should cook with gas directly, rather than with electricity substantially generated with gas turbines.
Last thing to look at would be time-of-day supply mix. Where I live, in Ontario Canada, the dinner hour peak supply is dominated by natural gas, but much of the rest of the day would be driven by nuclear and hydroelectric generation. (This is visible in daily reports from our Independent Electrical System Operator, ieso.ca.) Do I have to cook at dinner time or could I shift that to an all-day slow-cooker, supplemented with BBQ, microwave, etc?
The details matter and I recommend you get to know your regional electrical network well. It makes many decisions more straightforward and can affect your daily behaviour, too.
