Measuring economic growth from outer space

I love the satellite picture of the world at night - the one where Europe and America are seas of light, North Korea is invisible and the only lights visible in much of Africa are in South Africa and the oil flares in the Gulf of Guinea. Obviously, there is a strong correlation with economic development, or at least people having stuff to do at night.
J. Vernon Henderson, Adam Storeygard and Vernon N. Weil at Brown University take this insight a step further: why not use lighting levels to measure changes in development over time? This turns out to be a particularly useful method for countries where statistics are erroneous or missing, for example because of civil war. Governments can manipulate figures, but lighting never lies. Here are the two main findings (also summed up by the Wall Street Journal and Marginal Revolution):

1. Lighting is indeed a proxy for economic development and it goes down as well as up: there are some great pictures of changes in lighting levels in Eastern Europe in the 1990s. Whereas Poland experienced economic growth of 56% and an increase in lighting of 80%, neighbouring Ukraine saw its economic activity decline by 35% and lighting fall by 47%.

2. Increases in agricultural productivity (from high rainfall years)raise economic activity and hence lighting in nearby cities. Are these farmers rushing to sell their goods at the market, buy TVs with the earnings or simply celebrating their good fortune at the bar?

I'd love to see some further work on this data set. One question I have is whether the data might be distorted by certain high-light activities: mining, for example, or oil refining. This might matter for, say, DR Congo, where light levels seemed to increase in the 1990s, in the middle of a devastating civil war. I'd also like to see the impact of power cuts, such as California experienced a few years ago or South Africa in 2008. Most power cuts don't last long enough to show up in GDP figures, but their short-run effect might be severe: think of what happened in Europe this January when Gazprom turned the heating off. Next time that happens, we might be able to measure its effect from outer space.

Climate change migrants in Ghana

When you travel north in Ghana, the climate becomes drier and the villages poorer, until you end up in the Upper East and Upper West regions - friendly, slow-moving places, dry for most of the year and becoming more so. In other words, exactly the sorts of places where you would expect climate change-related migration to begin.

Sam Knight in the Financial Times tries to unpick the climate change migration debate. Is climate change migration something entirely new, or merely a continuation of existing trends? It looks like the numbers will be greater than we have been used (the Stern review suggests anything between 200 and 500 million people over the next 50 years), but that doesn't mean that starving farmers from Burkina Faso or Bangladesh will be pitching up in European capitals. More likely, the children of the rural poor will migrate to coastal cities and the educated youth of the capitals will migrate to richer countries, as they do now.

So what can we do about it? Beyond the obvious priority of containing climate change, I can think of two helpful policies:

1. Invest in agriculture in vulnerable areas - whether it's drought-resistant seeds, irrigation, new kinds of crops that reduce soil erosion or thrive in drier (or more volatile) climates
2. Improve transport links between coastal and inland regions: that facilitates seasonal migration, which keeps remote areas alive through remittances and periodic visits. It will also bring down the cost of living and make it easier for people in the arid areas to sell whatever they grow to richer urban consumers

On the other hand, these two are unlikely to work:
1. Trying to restrict migration - through passports, ID cards, quotas, . People will still move, only they will pay more for it and people traffickers will collect the difference
2. Bribing people to stay at home through welfare payments, social services, etc. Investing in health and education in rural areas is a great area, but it's more likely to promote migration than discourage it

Climate-induced migration is nothing new: we've been at it since the Sahara was green. It may be that the last few millennia were the abnormality and human migration patterns will end up looking more like they did before we invented agriculture.