Soaring CO2 level reports should be treated ‘with caution’

By Ed King

Reports of dramatic rises in the levels of heat-trapping carbon dioxide in the atmosphere should be treated with caution, a leading climate scientist has told RTCC.

Earlier this week the USA’s National Oceanic and Atmospheric Administration (NOAA) published readings from its Mauna Loa weather centre in Hawaii, revealing CO2 levels had risen by 2.67 parts per million since 2011 to total just under 395 parts per million (ppm).

This number is significant as it is edging closer to the stabilisation level of 450ppm that certain studies say is required to limit warming to 2°C above pre-industrial levels, a target scientists suggest could prevent climate change spiralling out of control.

As a result, some reports on NOAA’s findings concluded they meant it was ‘very unlikely’ this level of warming could be avoided.

But Bill Collins from Reading University’s Department of Meteorology and a contributor to the Intergovernmental Panel on Climate Change’s forthcoming review on climate science, told RTCC data gathered over a short period could be misleading.

“I would urge caution about treating any one year as telling us something really special,” he said.

“There has been a big deal made of this being the second highest annual rise ever – but there is quite a lot of variability in CO2, due to plant ecosystems, so the last highest rise was after a very warm year.

“That was 1998 and not basically due to man-made causes but because it had been a hot year and the soils had given off a lot of CO2 and the plants had not grown strongly – so the year to year variability is often caused by the uptake of plants and trees.

“That’s probably why we have a big increase this year.”

Measurements at Mauna Loa are taken from air samples in a remote area that NOAA says has ‘minimal influences from human or natural activity’.

Collins says data from the observatory are particularly relevant because it has the oldest records of atmospheric carbon dioxide levels dating back to the 1950s.

In an email to RTCC US-based climate scientist Michael Mann pointed out the latest data suggests CO2 levels are now above the IPCC’s ‘standard emissions scenario’ laid out in its fourth annual review in 2007 (see graph below).

“This latest CO2 measurement indicates that CO2 concentrations are running above the standard scenario climate change projections that are typically depicted in the IPCC report,” he said.

Climate scientists often complain that too many ‘value judgements’ are made linking global warming with extreme weather events and other climatic extremes, arguing assessments need to be made over decades rather than days, weeks, months or individual years.

It’s a rule that applies both to sceptics who cherry-pick data and also to campaigners who leap on a storm or typhoon and brand it as evidence to back up their theories.

But as a recent paper from the UK’s Met Office on the 2011 East Africa drought reveals, there is growing evidence that rising global temperatures are increasing the frequency of extreme events.

Collins stresses the importance of taking a variety of factors into account when assessing this issue, while acknowledging that most current trajectories point to an atmosphere that is becoming increasingly packed with CO2.

“At the moment we’re not following any of the lower trajectories, which is where we would hope to be. There’s no doubt that is worrying – we are currently on the wrong path,” he said.

“What we need to look at is the overall and longer term trend. Take a lot of years in context – basically we’re pumping a lot of CO2 into the atmosphere than we ever were before.

“It’s a bit like we say about the weather, one hot summer doesn’t prove global warming, but if you have lots and lots of them.

“All the signs are that we are increasing carbon dioxide levels and the fact that these figures have emerged just adds to the story – but it’s not a story in itself.”