Skip to navigation | Skip to content

Global warming confirmed: new research


It's confirmed: we are making an impact on the Earth's temperature.

Research based on statistical analysis rather than climate modelling has confirmed that over the past 130 years, human activity has caused the Earth's surface temperature to rise.

"This is a very different method to what other people are using," explained Dr David I. Stern, from the Australian National University's Centre for Resource and Environmental Studies, who conducted the research.

"It strengthens the case because the more methods people use to get the same result, the stronger the case gets."

Dr Stern worked with Dr Robert K. Kaufmann, of the Centre for Energy and Environmental Studies at Boston University. Their work appears in this month's Journal of Geophysical Research (Atmospheres).

Most climate assessments are made with simulation models where predictions are measured against what has actually happened. This research took a different path.

"We are doing a statistical analysis — looking at the relationships between sets of data," said Dr Stern.

The time period the research covers was restricted by available data. "They first started measuring atmospheric temperature on a widespread basis in about the 1850s and 1860s," he said.

But it is not as simple as just measuring atmospheric temperature. There are many mitigating factors when trying to evaluate the impact human activity has on the Earth's surface temperature.

"It's not a simple story, you need some sophisticated statistics to try and work out what's going on," he explained.

The researchers had to allow for fluctuations in temperature due to the ice age cycle, the Earth's orbit, and the number of sunspots on the sun.

Sunspots are dark patches on the sun that appear every 11 years. Their presence results in more radiation activity in the sun and the sun appears brighter. This, in turn, raises the temperature on the Earth.

"Since the 18th century, when there was a little ice age, and a minimum number of sunspots on the sun, the number of sunspots on the sun have increased," explained Dr Stern.

In addition, the Earth is cooling down very slowly towards the next ice age. Ice ages are a result of the 'wobble' of the Earth around its axis, which affects the seasons.

"That pretty much drives the long cycles of 100,000 years — the ice ages," said Dr Stern.

The last ice age ended between 20,000 and 10,000 years ago. "Temperatures reached a maximum about 5,000 years ago, and since then they have fallen, with some ups and down, and we are on the upswing again."

The research looked at the two hemispheres separately. Pollutants such as carbon dioxide, methane, and other gases last in the atmosphere a long time so they are spread more or less evenly all over the Earth.

"The big difference between the two hemispheres is the emissions from industry, particularly sulphur dioxide," explained Dr Stern.

Sulphur dioxide does not last long in the atmosphere, which means it gathers into clouds and falls back onto the continents in the northern hemisphere where most of the emissions are produced.

"The effect in the southern hemisphere is very little."

The clouds cause a cooling effect in the shorter term, the reason why temperatures cooled in the 1960s and 1970s. The researchers found that this masked the human impact on greenhouse gases to some extent in the northern hemisphere, but warming was easier to detect in the southern hemisphere.

Moreover, restrictions on sulphur emissions were introduced in many countries in the 1970s to curb acid rain, and this has allowed the warming effects of human greenhouse emissions to become more apparent.

"Certainly in the last 50 years you can see stronger and stronger the signal due to human effect," said Dr Stern.

"[The temperature] was increasing anyway, but now it has started increasing a lot."

In the last century, the temperature increased by 0.5 to one degree, while predictions of climate change in this century due to human activity range anywhere from two degrees to six degrees.

"It's a big range of predictions," said Dr Stern.

"As each year of data comes in, we can see more clearly that people are affecting the climate."