Using a coupled global carbon-climate model, Scott Doney of Woods Hole Oceanographic Institution in the US and Philip Boyd of the University of Otago, New Zealand and colleagues, quantified anthropogenic climate change relative to background natural climate variability in the Southern Ocean over the entire 21st century. They found that the rate of manmade climate change will not exceed background climate variability over the next few decades. What’s more, the predicted rates of change are too subtle to be mimicked experimentally at present.
The team says this is because phytoplankton need time to respond, and therefore adapt, to any change in climate. "For adaptation to change to occur, the change must be sustained," explained Boyd.
Most studies to date into the effects of climate change on organisms either use results from global model simulations or perform experiments in which the environmental properties of seawater containing phytoplankton are altered rapidly. In the new study, the New Zealand-US researchers combined these two approaches. The coupled ocean atmosphere model they employed was able to "tease apart" the relative magnitude of the climate change and climate variability signals in the Southern Ocean.
"We could then compute the decadal rate of change – both its magnitude and sign – for a wide range of environmental properties that phytoplankton are sensitive to," Boyd told environmentalresearchweb. "We compared these rates of change with the rates of change that have been used in conventional experiments in which these environmental properties have been altered rapidly."
Boyd explained that since we cannot put too much store on detecting the biological effects of climate change over the coming decades, it may appear that all is well in the Southern Ocean during this time. Only after a period of 30 years or so, when there has been a sufficient increase in the climate change signal for it to override the climate variability signal and sign, will the effects be discernible. These effects, for example phytoplankton fixing more or less carbon, could be unanticipated – and even rather sudden – at this time.
"We have to reassess our current way of doing experiments to look at climate change – where we alter, overnight, all the environmental properties in seawater to which phytoplankton has been added," said Boyd. "This tells us little about how cells might respond to gradual change due to climate change."
Instead, determining the resilience of different species or groups to an envelope of conditions is a better technique, he added. There are even clues in geological records that could help, and these could be linked with better-designed contemporary experiments.
The results were published in Biogeosciences.