My guess is: education for girls in Africa.
Why? Carbon emmissions per year come down to
(energy use per person per year)(carbon emitted per unit energy)(number of people).
In developed nations, all of these terms are stable or declining. In many developing nations, and Africa in particular, population growth is still exponential. Relatively small changes in the exponent of that growth have huge impacts on future carbon emission.
The pattern of decreasing fertility rate as modern societies develop is called "demographic transition". One of the biggest factors driving demographic transition is increased education levels for girls.
So to get the biggest multiplier on future carbon emmissions, look for the fastest growing term of the equation (population); look where it is growing the fastest (sub-saharan Africa), and look for the best way to reduce that growth (education for girls.)
(Of course, education in poor countries is beneficial and worthwhile regardless. But if you have to decide between investments in education or public health in a poor country, I've gotten the impression there's lower-hanging fruit in public health.)
For that country's carbon footprint to just remain stable, they will have to halve the amount of carbon emissions per person every 20 years.
This means that these countries will need to completely replace their infrastructure with technology and processes that are twice as efficient every 20 years, just to keep their carbon emissions stable.
I just don't see any way for technology and infrastructure to outpace population growth that fast.
Most realistically with population growth this high, there is probably going to be an explosion of carbon emissions regardless of how much green technology is rolled out in parallel.
Even if your assumption is true, it doesn't negate the fact that [some people] in the western world need to stop spewing/believing inane lies about global warming, so we can all start doing our part, as a society and as a system.
No, population growth across Africa as a whole is accelerating:
In the past year the population of the African continent grew by 30 million. By the year 2050, annual increases will exceed 42 million people per year and total population will have doubled to 2.4 billion, according to the UN.
A virtuous circle. And the same that's at work in all more-developed countries.
I previously wrote "racist". This is worse. I don't know the word for what this is.
Nobody is forcing African girls to have fewer children. If you'd like to discuss, I'd love to hear your argument on why you think that giving African girls more choices than "bear four kids by the time you're eighteen" is bad.
No where, to fight climate change the single best thing to do is curb your consumption and save money. Don't buy new gadgets every year, don't go on holidays far away, don't buy expensive meat, take public transport if possible, don't buy a huge house, don't use air-con. Do all that and you've prevented more carbon emissions than a small African village will ever produce and you'll save money.
I'd wager getting out poverty causes both education and fertility to improve and that is the real driver in this study.
How quaint. I have a sneaking suspicion that long after we've choked ourselves out of existence there will still be plenty of life flourishing. Nature will find a way without us. We'll just be a little nasty blip on the geological scale of time.
The planet isn’t going anywhere. We are! We’re goin’ away. Pack your shit, Folks, we’re goin’ away. We won’t leave much of a trace either, thank god for that. Maybe a little styrofoam, maybe, little styrofoam. Planet’ll be here and we’ll be long gone. Just another failed mutation. Just another closed-end biological mistake, an evolutionary cul de sac. The planet will shake us off like a bad case of fleas, a surface nuisance. You wanna know how the planet’s doin’? Ask those people at Pompeii, who were frozen into position from volcanic ash. How the planet’s doin’. Wanna know if the planet’s alright, ask those people in Mexico City or Armenia, or a hundred other places buried under thousands of tons of earthquake rubble if they feel like a threat to the planet this week. How about those people in Kilauea, Hawaii who built their homes right next to an active volcano and then wonder why they have lava in the living room. The planet will be here for a long, long, long time after we’re gone and it will heal itself, it will cleanse itself ’cuz that’s what it does. It’s a self-correcting system. The air and the water will recover, the earth will be renewed, and if it’s true that plastic is not degradable well, the planet will simply incorporate plastic into a new paradigm: the earth plus plastic. The earth doesn’t share our prejudice towards plastic. Plastic came out of the earth. The earth probably sees plastic as just another one of its children. Could be the only reason the earth allows us to be spawned from it in the first place: it wanted plastic for itself. Didn’t know how to make it, needed us. Could be the answer to our age-old philosophical question, “Why are we here?” “Plastic, assholes.”
A letter from Gaia to humanity on the joy of expectation
Don't cry for me. When I let you evolve I knew it might cost the rhino and the tiger. I knew the rain forests would be cut down. I knew the rivers would be poisoned. I knew the ocean would turn to filth. I knew it would cost most of the species that are me.
What is the death of most of my species to me? It is only sleep. In ten million years I will have it all back again and more. This has happened many times already. Complex and fragile species will break along with the webs they are in. Robust and widespread species will persist along with simpler webs. In time these survivors will radiate to cover the globe in diversity again. Each time I come back in beauty like a bush pruned and regrown.
Be happy for me. Over and over again I have tried to give birth to more Gaias. Time and time again I have failed. With you I have hope. I cannot tell you how happy I am.
Your minds, spacecraft, biospheres, and computers give me new realms to evolve into. With your minds I evolve as ideas in inner space. With your technology I can evolve into self replicating habitats in outer space. Your computers and minds contain model Gaias I can talk to; they are my first children. Your space craft and biospheres are a step to spreading Gaias throughout the stars.
Cry, yes. Cry for yourselves. I am sorry those alive now will not live to see the splendor to come from what you have started. I am sorry for all the suffering your species and others will endure. You who live now will remember the tiger and the rain forest and mourn for them and yourselves. You will know what was lost without ever knowing what will be gained. I too mourn for them and you.
There is so much joy that awaits us. We must look up and forward. We must go on to a future - my future, our future. After eons of barrenness I am finally giving birth. Help me lest it all fall away and take eons more before I get this close again to having the children I always wanted.
In the US, there's still a large group of people (or maybe just a vocal group) that cover their ears and won't listen to anything climate-change related, even in the highest places of our government.
I hope a healthy dose of "this is what climate change looks like" will scare people into believing. Even if you don't want to believe that humans are the cause, we still need to do something about it, and fast (something besides blaming everything on homosexuals).
It's interesting how a lack of accountability over the weather is so deeply ingrained into our culture like this.
Not unlike the apathetic feeling that causes people not not show up at the polls.
Getting political consensus here would be nice. But individuals can lead by example by living more sustainable lives.
If I have the personal will to devote an hour a week or $20 of my budget to sustainability, that energy is inordinately more effective when spent pressuring my boss to upgrade our fleet of derelict 4 mpg coal-rollers that do hundreds of miles a week, or writing a letter to my congressman to tryto convince him that global warming isn't a scam, rather than enduring the inconvenience of carpooling so that between my wife's 25mpg and my 30 mpg cars we can save 30 miles a week.
I can contribute a tiny part through personal life changes, or a big part through advocacy, with the same effort.
Now we're getting into the meat of the problem. If everyone worked less, got less money to spend on stupid plastic shit, drove less in our cars, threw away less perfectly edible food, and spent more time with the people we care about, both we the people and the planet would be better off.
But for our debt-fueled micro- and macro-economies, it would spell utter disaster. Financial crisis writ large. Housing market would go to shit. Banks would default. The state would get less taxes, so deficit would skyrocket. Meanwhile national debt, which is measured relative to GDP, would blow up much quicker than the deficit since GDP would drop sharply.
So nobody will ever actually make it happen.
When does Mr. Burns' Sun Blocker  become the most realistic opportunity for us to actually control warming?
When that starts happening in major cities, hopefully people notice before large numbers of the population have severe health problems from it.
By the time it gets destructive enough that effective mass action becomes possible, I fear it will be too late for us.
I have thought a lot about this and come to the conclusion it is to a great extent due to theological beliefs. A large proportion of Americans are evangelical Christians who believe the Bible is the literal world of God, and furthermore believe that the Bible says that unregulated free market capitalism is the right economic system.
So when scientists claim that unregulated capitalism is causing damage to the world that in turn is harmful to the human race, these people assume that this claim is wrong and the scientists are really atheists trying to undermine Biblical religion.
As for the libertarians and conservatives who just make scientific arguments, it seems to me they are assuming that the Earth was created such that unregulated capitalism can't possibly harm it,at least not in a way that would harm humans, no matter what new technologies corporations introduce, and on how large a scale. So they have a sort of implicit theology.
"Supplementary data are available at BIOSCI online including supplemental file 1 and supplemental file 2 (full list of all 15,364 signatories)."
Why? Because nobody cares enough (or believes deeply enough) to make radical lifestyle changes.
Al Gore still have several huge houses. Leanardo DiCaprio still takes solo jet trips across the ocean. The richest people (of all political persuasions) continue to live lives that don't reflect an austere lifestyle at all.
Why should anyone make sacrifices if nobody else does?
(ps: down-voting this post doesn't change this fact...)
A.) Is there a citation that accompanies your statistic?
B.) Does this number account for the type of scientist? Are you lumping non-Earth scientists (say, fiber optic researchers) in with your assesment that 15K is not a large number?
B) I just like to point out the hypocrisy (ref. OISM where 32,000 scientists where considering a "not a very compelling figure, but a tiny minority" (https://www.skepticalscience.com/OISM-Petition-Project.htm, together will all the left-leaning media's "breakdown" of this petition).
UN representative Christina Figueres has already stated in Brussel a couple of years ago that "global warming" has nothing to do with climate, but economy (i.e. "anti-capitalism"): https://www.investors.com/politics/editorials/climate-change...
And as a reminder: consensus !== science.
the OSIM data is less informative, would be interesting to compare trustworthiness:
This won't happen, because we want to live forever or that very least certain technological elites are trying to make that happen. We want to have all the latest technology regardless of the transportation costs (shipping containers). Be able to eat that latest restaurant. I could go on.
Climate change is real. How much is man-made? I don't know and I don't really care. On a personal level I attempt to keep my carbon footprint low, though I drive to work and eat meat daily - I bought half a cow and whole pig and store them in a deep freezer. At the same time I have had the same flip-phone for 3 years, and the prior to that I didn't have one. Have one TV in my house and a record player.
Reduce your consumption to your needs and a few wants, rib-eye steaks. Earth will prosper long after we are gone.
At this point I just ask what scientific statistic a person would need to hear in order to consider changing their mind. Unfortunately, I haven't ever gotten an informative reply indicating knowledge of the field, and am still open to hearing what exactly it would be.
Edit: Granted, at this point, most people on both sides seem to have given up learning about the fundamental literature driving this debate. See John Oliver's "It Just F*ing Is" on his recent show.
"Climate change is bullshit! I demand to see evidence of it actually occurring!"
<is presented volumes of data>
"I don't recognize these sources! These were payed for by liberal media! I demand to see real data!"
Rinse and repeat.
Truth is, although I strongly tend to believe climate change claims, I still feel some strong skepticism. I know my way around math, statistics, chemistry, and physics, but I couldn't tell you what measurements you actually can do to support climate change assertions. How do you measure the average temperature of a region, let alone the world, over a long period of time?! I've always felt uneasy about archeologists drawing conclusions from a single bone fragment, or even cosmologists drawing enormously long chains of conclusions from star spectra, but in those cases a) the measurement itself is obvious, b) the reasoning is obvious (even if you disagree with it) and c) it doesn't really matter all that much. Climate change, though, suffers from a) measurements that aren't obvious, b)reasoning that isn't obvious, and c) is incredibly important and we can't get it wrong. And moreover, if you express these doubts, the vast majority of climate change activists will just get angry with you and either stop talking to you at all, or point to letters with lots of eminent signatories saying, "it all makes sense to us, the evidence is overwhelming, we're really smart, so trust us."
Argument from authority isn't good enough, and the intuitive argument isn't good enough, either. Yes, we live in a thin skin of biosphere and we are releasing CO2 into the atmosphere at a huge rate in absolute terms. But I don't have an intuition about the relative rate, especially when compared to natural processes (which are vast). We cut down forests at a prodigious rate, which hurts capture, but I don't have an intuition about the amount of this either. I would love it if someone took these concerns seriously and wrote a book about it.
(For the record, I think there are other "good enough" reasons to change our behavior. Rampant consumerism isn't good for people or the planet in more obvious, directly measurable ways. Plus, even if the odds are low for a global catastrophe, it is better to be safe than sorry.)
Alas, many skeptics, even on HN, prefer to make general armchair-physics arguments despite the information already out there, condensed and edited, and backed by peer review and hundreds of citations into the literature.
Annoyingly, sometimes these skeptics even then complain that there is not enough information to really be sure, as if they have looked.
None. Your are trying to use reason to influence an emotional behavior. It won't work.
The day geeks understand, accept and practice this simple truth, everything will get easier. For everything. Love. Work. Politics. Raising children. Everything.