Cars still don't put out as much greenhouse gas as cattle does, and plus, cars today are both able to be much faster and much cleaner than the cars of the past. You couldn't buy your Lamborghini in California if it didn't fit their emissions laws.
Computer enthusiasts and gadget enthusiasts use a lot of electricity, and aside from solar panels, they don't have a lot of say in the type of power that is delivered to their house (and don't get me started on carbon credits, because those are a scam)
First, the limits set on California automobiles aren't nearly stringent enough to make a positive impact on lessening greenhouse emissions. Second, the myth that cattle is the leading cause is ludicrous, there are far more humans who emit more greenhouse gases in this world than cattle, so blaming animals for global warming is about as logical as blaming the sun (another myth the "right" seems bent on distributing). Third, carbon credits are not a scam. Simply put, they allow people to invest money into alternative energy sources. As you correctly stated, there are no other alternatives to conventional energy sources for homes other than local power companies. Carbon credits have gotten bad press from political spin, mostly millions paid by oil companies and their political counterparts/lobbyists, however the concept is to empower a free market for solar, wind and hydro power. People want to make money, so by logic creating investment opportunities in green energy will propel that industry. By determining how much energy a household consumes (along with doing everyone's part to limit energy waste), buying "credits" is simply a way of investing in wind, solar, hydro and other energy sources, with the end result being an established future alternative to current antiquated power companies.
Lastly, hydrogen fuel cell automobiles are already being tested and used through Honda by families in California. Using solar power to harness the hydrogen from water, these vehicles fuel in designated hydrogen stations that do not transfer the harnessing of hydrogen onto conventional power sources, thus staying "green". As of today, these vehicles produced by Honda (and GM, with the thanks of Senator Hillary Clinton in pushing for military vehicles in upstate NY to use strictly hydrogen) are obtaining 400 miles per tank, are just as safe if not safer in combustibility than traditional gasoline and produce only water vapor and/or pure H2O after the chemical reaction between the released hydrogen and oxygen that is naturally occurring in the atmosphere.
The truth is, now with nations such as China becoming the worlds biggest contributor next to the U.S. in the burning of fossil fuels and pollution, automobiles are the biggest contributor to greenhouse emissions coupled with the reality that overpopulation is taxing our natural resources and creating more dilemma's for the future. There are plenty of alternatives to coal and oil, if it were not for the control oil companies currently have the global warming and man's contribution to such would be greatly lessened.
Pick up a few books, read up on the issue, and don't just rely on information from Faux News or even CNN and MSNBC. Keep in mind who controls the media, individuals such as Rupert Murdoch and other billionaire philanthropists with personal vested interest in money making and political ties. Keep in mind the U.S. spent millions to convince American's that global warming is a myth, with this current administration forcing scientists to remain silent, as the current economy is dependent on oil. This administration, as any administration I suppose, wants to keep their numbers up within its current office. If politicians really cared about the people there would be a Pres. that would actively seek out alternative energy sources while ceasing the dependency on gasoline, but that would result in a drop in the current economical growth and stock market during their term. However, as time marches on the economy would surely rebound (as the pendulum often sways) to support a greener economy. It starts with each of us. I replaced all our appliances with new energy star compliant devices, such as dishdrawers that use less water and energy, and front loaded HE washers and dryers. Using timers and yes, even researching and investing in alternative energy sources through carbon credits (I would also like to know how that is a scam, as it has been proven that money invested through carbon credits goes directly to researching and funding alternative energy), is a good start, but not the only solution.
Again, educating oneself on facts and not propaganda is paramount in making a change. It starts with you.