(Cross-posted from Our World in Data.)
The world is much better. The world is awful. The world can be much better. All three statements are true.
Here I focus on child mortality, but the same can be said for many aspects of global development. There are many aspects of development for which it is true that things have improved over time and are terrible still, and for which we know that things can get better.
The world is awful
In the visualization below, I present three scenarios of child deaths. The blue bar represents the actual number of child deaths per year today. Of the 141 million children born every year, 3.9% die before their 5th birthday. This means that every year, 5.5 million children die; on average, 15,000 children die every day. 
Clearly, a world where such tragedy happens is an awful world.
The world is much better
The big lesson of history is that things change. The scale of these changes is hard to grasp. The living conditions in today's poorest countries are now in many ways much better than they were even in the richest countries of the past: Child mortality in today's worst-off places is between 10-13%; in all regions of the world it was more than three times as high [30-50%] until a few generations ago. It's estimated that at the beginning of the 19th century, 43% of the world's children died by the age of five. If we still suffered the poor health of our ancestors, more than 60 million children would die every year — 166,000 every day. 
This is what the red bar represents in the visualization below.
If you want to see how child mortality has changed, read Hannah Ritchie's post: From commonplace to rarer tragedy — declining child mortality across the world
Such large improvements are not limited to health; the same is true across other aspects of life (as I show in my short history of living conditions). In a number of fundamental aspects (obviously not all), we have achieved very substantial progress and know that much more is possible. These aspects also include education, political freedom, violence, poverty, nutrition, and some aspects of environmental change.
What we learn from this is that it is possible to change the world. I believe that one of the most important facts to know about our world is that we can make a difference.
(You can see a larger version of this graph here.)
The world can be much better
Progress over time shows that it was possible to change the world in the past. But what do we know about what is possible for the future? Were we born at an unlucky time in modern history, in which global progress has come to a halt?
Studying the global data suggests that the answer is no. One way to see this is to look at those places in the world with the best living conditions. The inequality in living conditions in the world today shows that there is much work left to do. If health across all countries of the world was equal, it would not be possible to really know whether further improvements are possible or how to achieve them. But the fact that some places have already achieved much better child health leaves no doubt: Better child health than the global average is not just a possibility, but already a reality.
So what would global child mortality be if children around the world became as well off as the children in those places where children are healthiest today?
The dark green bar in the visualization shows the answer. The region with the lowest child mortality is the European Union. The average in the European Union (0.41%) is 10 times lower than the global average (3.9%).
In the EU, 1 in 250 children die, whilst globally the figure is 1 in 25. If children around the world were as well off as children in the EU, 5 million fewer children would die every year.
Of course, a child mortality rate of 1 in 250 is still too high. It will be a major achievement if the world as a whole catches up to that level of health, but in the healthiest places we should also try to push the boundaries of what has been shown to be possible.
We should certainly not make the mistake of believing that it would be easy to reduce the global child mortality rate to that of the EU. For a society to achieve such good health, many development aspects have to improve; today's best-off countries achieved two centuries of slow, sustained economic growth that bought the infrastructure (housing, sanitation, public health measures) necessary for good health.
But while a better world cannot be achieved overnight, we learn what is possible from the best-off regions; in this sense, we know that these 5 million annual deaths are preventable. The fact that child mortality in entire world regions is tenfold lower than in the world as a whole shows us that it is possible to make the world a better place.
The world is terrible; this is why we need to know about positive change
It's easier to scare people than to instill confidence in them, and many writers on global development report on how awful the world is. I agree that it is important that we know what is wrong with the world, but given the scale of what we have achieved already and what is possible for the future, I think it's irresponsible to only report on how dreadful our situation is.
The world is much better. The world is awful. The world can be much better. We have to study the data to know all three perspectives on global living conditions. When we do this, these facts are impossible to miss. But the facts of how the world is changing are not known to most of us because many of the writers that report on how the world is changing do not take the data seriously. This needs to change.
What we have to achieve as writers on global change is to convey both perspectives at the same time: We need to know how terrible the world still is and that a better world is possible. This is what I hope to do.
If we had achieved the best of all possible worlds, I wouldn't spend my life writing and researching about how we got here. What keeps me going is to share the knowledge that change is possible — though not inevitable — and the wealth of knowledge that researchers around the world have acquired on how to make a better world for everyone.
We know that it is possible to make the world a better place because we already did it. It is because the world is terrible still that it's so important to write about how, in several important aspects, the world became a better place.
This work is licensed under a Creative Commons Attribution 4.0 International License.
Child deaths in 2017: 140.95 * (3.9/100)=5,497,050. This means 5,497,050/365.25=15,050 child deaths per day. Here I'm assuming that the cohorts of children younger than 5 are all equally large. As the number of births per year is not rising much anymore, this seems like a justified approximation that makes the calculation straightforward. ↩︎
We don't know how many children actually died at the time because I don't have estimates of the number of births globally for that period. We have estimates of both the number of births and the mortality rate for the 1950s and 1960s, and the records show that around 20 million children died every year. See the data shown here. ↩︎
[I'm doing a bunch of low-effort reviews of posts I read a while ago and think are important. Unfortunately, I don't have time to re-read them or say very nuanced things about them.]
I think a lot of EAs (including me) believe roughly this, and this is one of the best summaries out there.
At the same time, I'm not sure it's a core EA principle, or critical for arguing for any particular cause area, and I hesitate about making it canonical.
But it seems plausible that we should include this.
This is an emotionally neutral introduction to the thinking about solving global issues (compared to, for example this somewhat emotional introduction). The writing uses an example of one EA-related area while does not consider other areas. Thus, this piece should be read in conjunction with materials overviewing popular EA cause areas and ways of reasoning to constitute an in-depth introduction to EA thinking.