What Drives Human-Caused Climate Change?

When looking at the ways humans cause climate change, it is good to remember that we are talking about more than just emissions of fossil fuels. Humans change the land cover of the planet, planting, cutting down trees, putting up reservoirs and paving over land for roads. We also emit conventional pollution, causing black soot and aerosols that have differing (and debated) effects on climate.

There is one human factor that drives all of this. It’s not technology and it’s not GDP. It’s population growth. The Intergovernmental Panel on Climate Change (IPCC) only incorporates global population size and growth into its emissions projections, without disaggregating or differentiating between the emissions levels of different social or demographic groups. Poor people cause climate change by cutting down forests, slash and burn agriculture, burning wood and dung, burning kerosene, etc. There are far too many poor people (that is, more than zero). Rich people cause climate change by using appliances, driving cars, flying in airplanes, building dams. There are far too few rich people (that is, less than all).


Because the IPCC (and folks like Nicholas Stern) don’t treat population seriously when they measure and project climate change and its impacts, their documents are not as helpful as they might be. For example, when Stern did his famous review he used an IPCC scenario that had 15 billion people living on the planet in 2100. This naturally caused him to think we would both emit more CO2 and suffer more from the consequences.

So it’s always a good idea to refresh our view of what is happening with global population. Fortunately, the UN periodically publishes updates to its projections.

“According to the 2012 Revision of the official United Nations population estimates and projections, the world population of 7.2 billion in mid-2013 is projected to increase by almost one billion people within the next twelve years, reaching 8.1 billion in 2025, and to further increase to 9.6 billion in 2050 and 10.9 billion by 2100 (figure 1). These results are based on the medium-variant projection, which assumes a decline of fertility for countries where large families are still prevalent as well as a slight increase of fertility in several countries with fewer than two children per woman on average. ”

Their high variant yields a projection of 16.6 billion in 2100 while their low variant shows a prediction of 7 billion (rising and then falling over the remainder of the century). You pays your money you gets to pick which variant you believe–or which variant supports your position on issues affected by population.

Fans of population studies (both of you…) will already know that the UN adjusted its population figures upwards in 2010, mostly because fertility wasn’t decreasing as fast in some African and Middle Eastern countries as had been forecast previously. We’ll see.

The UN now says, “At the country level, much of the overall increase between 2013 and 2050 is projected to take place in high-fertility countries, mainly in Africa, as well as countries with large populations such as India, Indonesia, Pakistan, the Philippines and the United States of America. ” Notice who isn’t on their list? China…

We’ll talk about this more in the future, but I’m interested in hearing what people think about the UN’s predictions. I’ll leave you with this quote from a UNFPA publication, Population Dynamics and Climate Change (which is well worth reading, by the way):

“It is impossible to understand and reduce vulnerability without taking population dynamics into account. From acute, climate-related events like storms and floods to long-term shifts in weather patterns and sea level patterns, the impacts only become clear through an understanding of who is at risk, what the risks are to people rather than just to places and how these risks vary within and across populations. Vulnerability is unevenly distributed between men and women and between the young, the middle aged and the elderly.”

4 responses to “What Drives Human-Caused Climate Change?

  1. Their high variant yields a projection of 16.6 billion in 2100 while their low variant shows a prediction of 7 billion (rising and then falling over the remainder of the century). You pays your money you gets to pick which variant you believe–or which variant supports your position on issues affected by population.

    I can’t agree with this. At least as far as should, I suppose it’s usually true as far as what people actually do.

    In a case like this, the precautionary principle should be applied, and the highest projection should be used. Then, options should be considered to deal with that level of increase, while supporting the equally desirable improvement of lifestyle for all concerned.

    There are many resources available: for me what stands out is the exponential decrease in production costs for solar PV, as well as other technology potentially useful in providing the necessary for that lifestyle (e.g. Moore’s “Law”). The answer is to foster human ingenuity, by investing in quality technical and scientific education, and an order of magnitude increase in both lab-bench research, and industrial R&D.

    • Hi Tom…

      I read the posts you linked, I think you’re being way too pessimistic. There’s a bunch of new technology, and new applications of current technology, that IMO will work together with cost reductions in PV to keep the exponential decrease going. I don’t usually blog on it, but I’ve left some comments at Judith Curry’s blog. My guess is that, overall, the cost will continue its exponential decrease until it starts to curve off at around 3-10¢/watt peak.

      Probably based on concentrating with efficiencies around 40%. This may well use Fresnel lenses and be vulnerable to cloudy days, but there’s some intriguing work being done on materials with very high indexes of refraction, over 30, that might offer another option. The results reported were for microwaves (slightly sub-millimeter), but might be extendible to visible/UV wavelengths using appropriate particle-beam printing. Whether that could produce cheaper concentrators than using standard technology to produce 1-sun 4-layer film, I can only guess.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s