In the spirit of celebrating every success, but only to the extent the success deserves, I would like to celebrate something that is kind of hard to describe. The rate at which things are getting worse is slowing down. We’re not going downhill as fast as we once were. The fever is high, but rising more slowly. We’re still headed for the iceberg, but our speed is declining.

The most striking example of this positive-negative phenomenon is world population growth. We humans have more than doubled our numbers since 1950 and will add 77 million more of ourselves this year. The equivalent of France plus Belgium plus Switzerland. The equivalent of the Philippines plus Laos. The equivalent of five Mexico Cities. This one year. China will grow by 12 million persons; India by almost 20 million; Africa by 19 million. The United States will add 1.4 million through natural increase and another 1 million to 3 million through legal and illegal immigration.

Lovable, full of potential as each human may be, no one I know thinks that adding more of us to this crowded planet helps us solve any problems. Many think that population growth makes all problems, from poverty to pollution, impossible to solve.

So here’s what’s worth celebrating. In the mid-1980s, we were growing not by 77 million but by 87 million a year. In the mid-1970s, the average woman bore 3.9 children; now the average is 2.8. The richest populations average only 1.9 children per family, below replacement level. Most industrialized populations have stopped growing or are slowly shrinking.

No one really knows why birth rates are going down, though family planners, economic developers, educators, and feminists are all happy to take credit. Whatever the cause, it’s a trend worth celebrating. Though the population is still growing.

Here’s another slowdown in a bad trend. For the past two years, the amount of carbon dioxide we have spewed into the atmosphere from fossil-fuel burning has gone down. It has been a tiny drop, less than 2 percent. To stabilize the climate we need to cut emissions by 60 to 80 percent. The carbon-dioxide content of the atmosphere is still rising. The earth is still heating up. But at a slower rate.

The causes of the carbon reduction are multiple. The collapse of the Soviet Union is a major one. As its sloppy coal-burning industries shut down or were refurbished, Eastern Europe’s carbon emissions dropped by 30 percent. Western Europe’s emissions, because of carbon taxes and efficiency technologies, have dropped 0.7 percent. The United States is going the wrong direction; its emissions have risen more than 10 percent since 1990. China’s went up over the same period by 28 percent, India’s by 55 percent.

But China’s carbon emissions are not growing anywhere near as fast as its economy. That’s because it is steadily replacing dirty coal with natural gas. Its greenhouse gas emissions and local air pollution are getting worse, but not as rapidly as we might expect. Semi-good news.

Throughout the 20th century, human water use rose twice as fast as the population. The water curve is not rising as quickly as it was, however; in some places it is even turning down. U.S. water withdrawals peaked around 1980 and have since fallen by about 10 percent. Our industrial water use went down 40 percent, partly because of the export of heavy industry to other parts of the world, but also because of water regulations that made efficient use and recycling economically attractive, legally mandated, or both. Irrigation went down partly because of increased efficiency, partly because expanding cities bought water away from farmers (and therefore took land out of food production), and partly because wells went dry. Per capita water use dropped wherever higher water prices cut waste.

Water tables are dropping more slowly than they used to be. That’s some sort of progress.

World fertilizer use has stopped going up, though it is still high enough to cause plenty of air and water pollution. The Soviet collapse helped stop the growth curve, as did European water quality mandates and the rise of organic agriculture. There’s still more fertilizer leaching into wells and lakes than is good for ecosystems or people. But in many places there’s less fertilizer pollution than there used to be, with little or no decrease in crop yields.

The 431 nuclear power plants now operating in the world will probably be a historic peak. From now on at least as many old reactors are due to be decommissioned as new ones are due to come into service. We still have an accumulation of nuclear wastes that we have no idea how to handle. It will continue to grow as long as any reactors are operating, and it will remind hundreds of future generations of our 50-year burst of irresponsible enthusiasm for this technology. But radioactive wastes will be piling up more slowly.

It’s hard to feel celebratory when the rain is slowing but the floodwaters are still rising; or we’re losing altitude but we’re no longer in free fall; or our diet is not taking off extra pounds, but is slowing the rate at which we put on more. Things are still getting worse. But we have turned a corner. It does begin to be possible to believe that we actually could start making things better.

That’s worth a celebration.