The biggest-impact action Mankind could take to correct the climate crisis woes of Global Warming and pollution is the one which isn't being publicly discussed these days.
The Earth's main problem of the last 100+ years is simply: overpopulation of us people.
Think about it; during the Industrial Age, the world's human population was roughly about 1 billion people. Which, it took eons to get to that amount. Roughly over the span of about the last 100 or 150 years, as Mankind has now arrived well-into the Information Age, the world's population has become 6.5+ billion people and growing.
Ordinarily that many people on the planet might not be a problem, per se. But, the hitch is that whereby a small percentage of people ("only" hundreds of millions) were once needing to use the world's resources, and polluting the planet in the process in order to live civilized in a "developed world", that percentage is currently expanding greatly and quickly.
So now, basically, everyone's proverbial "Slice of the Pie" has to get smaller, to accommodate all the rising standards of living. Which entail more individual private homes, everything which goes into running and furnishing that house, and the transportation to and from that house for work and gathering lives needs like food and clothing.
That said, don't get me wrong; improved standards of living is a paramount aim of all peoples. It just so happens that when 6.5+ billion people are all striving toward that, that the planet notices the effects. Effects which manifest themselves as over-pollution contributing to health problems of people, species, eco-systems and weather patterns of the planet.
The Earth is basically "crying Uncle" now; it's had all it can take of the stresses and strains of accommodating the now-multitude humans living upon her, in the wasteful and often-polluting manner in which generations of people have. And so, in recent years scientists have witnessed, politicians have finally been made aware and now religions have all finally taken notice of extreme and rapid changes occurring in the environment, conveniently coined Climate Change and/or Global Warming.
The real challenge, in my humble opinion, is to begin to (re)educate--because this is not a new idea--the world that over population is not a good thing. However, no religion, nor country, nor race wants to concede nor recede its numbers. Because there's strength in numbers. It's one way of self-defense, or atleast intimidation; having more of "us" than of "them".
Some religions flatly eschew the concept of practices meant to control one's population (yes, Pope, I'm talking to you. And before readers get upset, I'm a [former] Roman Catholic of Italian descent, so fahghetaboutit...). Additionally, what politician would really run on a platform of slowing down the birth rates in their country, in order to eventually scale-down the size of their nation's overall population in order to be more environmentally-friendly over time? Not many. Since that gets back to the notion of wanting more "us" than of "them" mindsets. (China was "forced" to do this with their one child policy. What if that policy came to Western cultures/countries in the next decade, huh?)
Back to my metaphor of everyone's Slice-of-the-Pie becoming thinner and thinner. My unease with much of what guilt-laden western cultures are undergoing now (yet once again...) by Reducing, Reusing, Recycling is that it may all be for naught someday. Especially if the world population doubles to about 12 billion people, nearly half of whom might live in mid to high standards of living (owning homes, cars, gadgets, becoming conspicuous consumers...).
It really seems that we're all just simply shifting the energy consumption needs from one side of the globe (Western worlds) to the other (Eastern worlds) this century. The resources drain (oil, water, wood, crops, seafood, oceans, etc) will continue unabated, and pollution will continue (coal burning, oil burning, nuclear waster disposal needs, etc...). And ultimately the world will, in effect, not have truly solved the root causes of Global Warming (Climate Change).
My small "big-idea" is that the world needs to really actually first get population growth to be in decline; maybe by 25% or 50%. Then the tenets of Reduce, Reuse, Recycle combined with green renewable energy sources like Wind, Solar, Hydro, Geothermal, Cellosic-based liquid fuels (and maybe "clean coal"?...) could continue to be woven into lifestyles of this and future generations. That might be really what it takes to finally stabilize pollution caused by Mankinds' daily living needs.
Natural population reduction a big idea that I haven't heard leaders seriously and consistently espouse. Because, as everyone wants to sit at the table to have some of the "High Standard of Living Pie", each person's slice can only just be a sliver, in order to even have enough pieces to go around for everyone to enjoy.