May 12, 2012 — andyextance

Researchers have confirmed a relationship that is making climate change tough to fight: economic growth and atmospheric CO2 concentrations have been tightly linked for the past 50 years. That’s what the University of Michigan‘s Edward Ionides and co-workers found by looking at levels of the greenhouse gas and gross domestic product (GDP), an important measure of countries’ financial performance, at a worldwide level. “GDP growth is like a proxy for CO2 concentration growth,” Edward told Simple Climate. “Under business-as-usual conditions, these two quantities are measuring essentially the same thing. This highlights a problem with using GDP as a measure of progress.”

Until now, much research on the link between CO2 and economic growth has looked at figures for each country. Some think using each country’s CO2 emissions separately “should be more informative”, Edward said. But there are problems with recording emissions accurately, plus goods or services used in one country often result in CO2 emissions in another. So, with Michigan colleague José Tapia Granados, and Óscar Carpintero from the University of Valladolid, Spain, Ionides went to the worldwide level for “a new and simpler perspective”.

As well as the total of all countries’ GDP, they used precisely measured atmospheric CO2 levels, rather than the more uncertain emission figures. “In addition, concentration of CO2, rather than the level of emissions, is the variable directly determining the global climate,” Óscar said. “Change in the atmospheric concentration is the result of emissions – mainly from burning fossil fuels, since natural emissions from volcanoes are estimated as a tiny fraction of man-made emissions – minus removals by natural sinks.”

Regression session

The team studied how the world’s GDP (WGDP) plus population, volcano eruptions, and the El Niño southern oscillation (ENSO) climate cycle influenced short-term, year-to-year changes in atmospheric CO2 concentrations. In the data, which covers 1960–2010, these concentrations have increased on average by 1.45 parts per million (ppm) per year. Measured by what dollars were worth in the year 2000, in the same period, the WGDP grew by $0.68 trillion per year on average. The world population expanded annually by an average of 76.3 million in that time.

To study how the different factors affect CO2 levels Óscar, Edward and Jose wanted to use a method called linear regression. This adds each influencing factor together after multiplying them by different “coefficients” in a way that most accurately reproduces the changes in CO2. Those coefficients can be positive or negative, but the larger they are the more influence the factor they are multiplying has on CO2 concentration. Then, a mathematical estimate of error for each coefficient determines how reliable the evidence they provide is.

To do the linear regression for short-term changes, the team had to use other mathematical methods to remove any steady long-term trends, leaving year-to-year variations. But CO2 levels, WGDP and population all grew faster towards the end of the 50-year period than they had at the start, which made their analysis more difficult. Another complicating factor came because there may be a delay between events that influence CO2 levels happening and their effect becoming measurable. And so these “lags” also had to be factored into the calculations, published online last month in a paper from the August issue of research journal Environmental Science and Policy.

Measure found wanting

Edward, Jose and Óscar’s results, show changes in WGDP have a significant effect on CO2 concentrations in the same year. For each $1 trillion that WGDP moves away from the trend, atmospheric CO2 concentration moves away from its trend, in the same direction, by about 0.5 ppm. There was also strong evidence that ENSO activity was also linked to short-term CO2 level changes, after a lag of one year. However, short-term population changes did not affect CO2, while the evidence linking major volcanic eruptions to CO2 levels was not strong.

The CO2-WGDP link would make it hard to reduce greenhouse gas emissions and therefore fight global warming, as long as countries strive to increase GDP as they currently do. “If ‘business as usual’ conditions continue, economic contractions the size of the [current] Great Recession or even bigger will be needed to reduce atmospheric levels of CO₂,” Jose said. He warns that, instead of continuing with “business as usual”, it might be necessary to change how the world’s economies work. “One solution that has promise is a carbon tax levied on any activity producing CO₂ in order to create incentives to reduce emissions,” he said.

The researchers are now looking at whether GDP does a good job of assessing how well countries are doing in other areas. “We are showing that GDP growth is not strongly linked to health progress in developed countries, indeed fluctuations are negatively associated,” Edward said. “For example, age adjusted mortality rates are typically above trend in economic booms and below trend in recessions. It is not clear how to quantify “good” economic progress, even once the deficiencies of GDP in this regard are recognized.”