Bill Gates proves that one person can make a difference—if he happens to be the richest person in the world. Since forming the Bill & Melinda Gates Foundation—and especially since leaving Microsoft in 2008 to dedicate himself full-time to the foundation’s work—Gates and his wife Melinda have emerged as two of history’s most powerful philanthropists, funding efforts from polio eradication to sewage-treatment plants, and setting the agenda for aid organizations around the world. They have convinced 127 fellow billionaires to sign their giving pledge, an oath to donate the majority of their wealth to philanthropic organizations. Today, the Gates Foundation has an endowment of $42 billion, almost four times the size of the Ford Foundation, and it distributes between $3 and $4 billion every year. As WIRED Science writer Maryn McKenna put it a few years ago, “Where Gates goes, governments and the media follow.”

So when Gates releases his annual letter each January, summarizing the foundation’s progress and laying out its priorities for the coming year, the world pays attention. Last year’s edition, a feisty debunking of “myths” about poverty, went viral. This year’s letter, co-written by both Bill and Melinda Gates and released today, is even more ambitious than usual. Titled “Our Big Bet for the Future,” it lays out a series of goals for the next decade and a half—cutting childhood deaths by half, eradicating polio and three other diseases, and making Africa capable of feeding itself, among others. Altogether, the letter predicts, “the lives of people in poor countries will improve faster in the next 15 years than at any other time in history.”

The letter is modeled on the UN’s Millennium Development Goals, a set of 15-year targets that expire this year and that Gates refers to as “one of the most important documents the UN ever did.” Representatives from every country in the world signed the goals in 2000, pledging among other things to reduce extreme poverty by 50 percent, slash child mortality by two thirds, and cut the maternal mortality rate by three quarters. Although not every target was reached—a full report card can be found here—the document is generally credited with focusing global aid efforts and providing a yardstick against which they can be measured. The UN is set to introduce a new set of development goals this September, and some observers worry that they will be a disappointment rather than an inspiration. Writing for the Guardian, Kevin Watkins frets that the discussions to date have been “hampered by a paralyzing lack of ambition, weak leadership, and the absence of a credible agenda to galvanise public engagement.”

That certainly does not describe this year’s Gates letter, the most rabble-rousing edition to date. Toward the end, the Gateses announce Global Citizens, a new program to educate and inspire action among the general public. “We want to give global citizens a way to lend their voice, urging governments, companies, and nonprofits to make these issues a priority,” the letter explains. In particular, the Foundation will ask its Global Citizens to push for a meaningful reboot of the UN’s Millennium Goals, and to hold their governments accountable for meeting those targets. It’s a surprisingly populist approach for the Foundation, which has tended to turn to billionaires for the bulk of its support.

In a wide-ranging phone conversation, WIRED spoke with Gates about this year’s letter, global inequality, and President Obama’s tax proposals. The interview has been edited for length and clarity.

__The UN is working on its update to the Millennium Development Goals. How do you think it’s going? __

We’re definitely on track. It will be a much longer document, and a broader set of goals than the MDGs were.

But the MDGs were so powerful because they were so succinct. Do you worry that if these goals become too broad, it will be harder to keep people focused?

That absolutely is a concern that I have. Then again, there are unfinished MDGs, and they will always have a very unique position. Key things like child health are so critical. If you have malnutrition you can’t do education very well.

I do think the new document will be so long that fewer people will read the whole thing. Then again, when we talk about books like the Koran or the Bible, not everybody reads every word of those things. I think of the MDGs like the Ten Commandments.

You operate from the belief that the world is radically improving in the fields of health, agriculture, and poverty. But there’s one area that you flick at in this letter where things seem to be getting worse, and that’s climate change. We’ve just learned that 2014 was the hottest year on record. Tech solutions are being developed, but they’re facing headwinds—be it political stagnation or extremely cheap gas prices. Do you have the same sense of optimism when you look at energy?

I have billions invested in various energy-related things—like battery companies, or cheaper ways of making electricity. I have a company that’s working on something called fourth-gen nuclear, this new super-safe nuclear design. So I think it is feasible to have energy sources that are even cheaper—although, as you say, that benchmark gets tougher as the price of natural gas and oil are so low.

There’s no doubt that we’re going to have some warming even as we start to deploy these solutions, because of the lags in the system. Nathan Myhrvold has written a few articles on this, about how even if you do the right things you still have some locked-in change.

I’ve been a big proponent that rich world governments should raise their energy R&D budgets. It is possible—based on the basic science of big energy, nuclear fuels, the photons that hit the earth from the sun—to have cheap energy. In the meantime we have to do some adaptation, which is mostly investing in agricultural systems so that farmers in the areas that will be most affected can have enough productivity and enough storage so that if they have lean years, their kids are not significantly malnourished.

__You’ve dedicated a ton of resources to delivering vaccines to remote areas of the world. It must drive you nuts when people in the rich world choose not to vaccinate their kids. __

I just read this book called On Immunity: An Inoculation—which is so well written, it’s unbelievable—that talks about this. It’s a little bit unsurprising considering you’re saying to parents, “Hey, take this needle and inject it into your kid! Honestly, we’re sure that it does no harm!” It really takes explaining to people why this is not only beneficial to their child but to society as a whole.

The anti-vaccination crowd, it’s very unfortunate. They create risk and in some cases there have been pertussis-based deaths and measles deaths. Those are the two that show up pretty quickly when you get any group of kids that haven’t been vaccinated. People thought, “OK, we have the Internet, information will get out there.” But misinformation got out there as well.

I do think we’ll keep vaccination rates high in the US. Rationality will succeed. But it will take cases like this Disneyland thing to remind people how irresponsible it is. The science about the safety is very, very strong.

Another source of discouraging data: income inequality. You’ve read Thomas Piketty’s Capital, and had nice things to say about it. But you also said that some inequality is built into the capitalist system, and the question is when it begins to do more harm than good. Has inequality become a hinderance?

I don’t think in some huge way. Of course, at a global level, income inequality is going down, because countries like China and India are getting richer much, much faster than the rich world is getting richer. So the overall picture on income inequality is very, very positive. And yet, each country has to look at the fact that, because of the nature of capitalism, there’s a tendency at the country level to have greater inequality unless you have tax policies to moderate it. So it’s a great democratic debate: What should those tax policies be? For the one country whose tax policies I know, the US, I’ve been in favor of more progressive tax approaches.

I also think philanthropy, although not a total solution to it, does moderate the problem. Especially if those who have been lucky give of their time and money to causes—like improving education or health—that speak to the most basic inequities.

So it’s a great topic for debate. A democracy is a self-correcting system, and over time I’d expect them to get it right. The founders were a little worried that the masses would get rid of capitalist incentives by going too far, but at least in the US that certainly hasn’t been a problem. The system has worked well for hundreds of years.

We’re speaking the day of the State of the Union. What do you think of the President’s tax proposals?

I don’t know the specifics very well so I really can’t comment. Just being pragmatic, the likelihood of a change in the tax system is fairly low. But I’ll be very interested. He no doubt will be promoting things that are progressive in nature so it’ll be interesting to see what he picks.

Let’s talk about your Global Citizen Initiative. This seems like a departure for you. How did it come about?

Some 6.5 million children die every year. There’s a subset of that where there’s an earthquake or flood, and people are so anxious to give and help. It reminds you that when people can connect and have an image of what’s going on, in those acute situations, they care and are willing to get involved. But 98 percent of childhood death comes from chronic, ongoing things, not those headline, one-time events. It’s malaria every day, diarrhea every day, pneumonia every day. The idea is that, if you sign up, on an ongoing basis, a few times a month we’ll give you an update on how things are going. It won’t just be a headline about an earthquake.

The idea is getting people to use their voice to say their governments should continue to be generous on aid. We're dealing with tight budgets. Even countries that have been generous, like the Netherlands or Australia, have made cuts to their aid budgets. And within the universe of NGOs, some are agricultural, some are environmental, some are health, you can pick one of those that you want to dive down into and get involved with.

That is a new thing. We’re not sure how well that will resonate. But we do think people’s basic morality, the desire to care about humanity broadly, that it’s fairly timely. There’s a bit of a vacuum there. There’s not an alternate way for people to grab on and see how they might contribute more.

At the same time, critics have grown dismissive of “clicktivism,” little bursts of online activity that don’t result in any sustained commitment or change. How do you keep this from being a mile wide and an inch deep?

The starting point is very shallow. But the beauty is you can use that to get in more deeply. If you sign up to be a global citizen, we won’t send you too much email but we’ll say, “Hey, if you’re interested in going to Africa, not only can you do some interesting fun things, but you’d have a chance to get exposed to these issues, see this stuff on the ground.” Once you do that, people tend to get hooked. They’ll see something and latch onto it—a particular village or disease.

But you’re right. Just because we have 10 million global citizens who give us their email address, that’s not our final metric. That’s a starting metric. The metric I care about is people who get involved in real activism, really take trips, really start donating and volunteering. This is just a gateway toward deeper involvement, if we do our job right.