Rapid climate changes that cause glaciers to melt are linked to stronger monsoons, which causes changes to major plant systems in these monsoon regions.
Dr. Jeffrey Severinghaus and his colleagues were able to use old air in ice cores from Antarctica to look at the changes in oxygen isotopesIsotope: All atoms of a particular element contain a specific number of protons in their nucleus (oxygen contains 8 protons), but the number of neutrons may vary. These different versions of an element are called isotopes. Naturally occurring oxygen is composed of three stable isotopes, 16O, 17O, and 18O, with 16O being the most common. Since every oxygen atom has 8 protons, the three stable isotopes have 8, 9, or 10 neutrons.X in our atmosphere over the past hundred thousand years. Plants breathe out oxygen, and the type of oxygen they give off depends on the kind of water they are receiving and how they are interacting with the air around them. Changes in plant systems can help cause the oxygen in the atmosphere to be composed of either predominately "heavy" or "light" isotopes.
By comparing these oxygen measurements to records of monsoon strength, it was seen that monsoons tended to be stronger when the oxygen isotopes were lighter. The relationship is especially obvious during periods of abrupt climate change. For example, rapid warming after cooler periods is shown to correlate with lighter oxygen isotopes and stronger monsoons. Monsoons affect and are affected by a large area of the earth's plant-growing regions.
What Does It Mean?
This discovery shows that tropical rainfall (the monsoon in particular) changed dramatically, in a few decades or less, during past abrupt climate change. Rapid changes in climate are accompanied by shifts in the land-based water cycle and its interactions with plant life, particularly at lower latitudes. Specifically, events of large glacier meltdowns caused by rapid warming in the past were shown to correlate with patterns of increased monsoon strength in Asia and Northern Africa.
Changing climate can cause a variety of locally and globally scaled impacts on environmental systems. When these large changes happen on short timescales, the effects can be even more dramatic. Not only does this discovery help us understand how climate change has affected hydrological systems in the past, but it may help us to predict what changes in global rainfall patterns might occur in the future and how that may affect our current agricultural systems.
Why Is It Important?
This is important because abrupt climate change is asymmetric, with the northern hemisphere cooling while the southern hemisphere warms. It tells us that tropical rainfall will shift south if humans try to cool the northern hemisphere (say, by geoengineering) without also cooling the southern hemisphere. South-shifted rainfall belts could mean millions of people starving in Africa and Asia, where so many depend on the rain for agriculture and their livelihood.
This figure shows the way that monsoon strength and plant systems track together. The purple line represents the part of the oxygen isotope measurements from ice cores that are representative of plant systems. The green line represents records of monsoon strength derived from cave records. The downward arrows point to known cold periods that end in rapid warming, causing oxygen isotopes to get heavier and monsoon strength to increase.
Peer Reviewed Reference
Severinghaus, J., R. Beaudette, M. Headly, K. Taylor, and E. Brook, 2009, Oxygen-18 of O2 records the impact of abrupt change on the terrestrial biosphere, Science 324, 5933.