Since the late nineteenth century, the average temperature of the earth has increased by 0.3 to 0.6oC. Global circulation models (GCMs) predict that in the next 50 to 100 years, the temperature will continue to rise by 1 to 3.5oC. These models attribute the rise in temperature to increasing greenhouse gas concentrations in the atmosphere, a phenomenon that has been argued to be most likely anthropogenic in origin.
The long term climate record may hold the key to whether this temperature rise is part of the natural variability of the climate system or is due to an anthropogenic signal coming from our industrial, agricultural and urban activities of the last 150 years.
The paleoclimate record, obtained from Vostok ice cores, shows that the average global temperatures oscillates naturally through time with certain characteristic periodicities. The troughs and peaks indicate the glacial and inter-glacial eras, respectively. Based on these periodicities, the present period with its characteristic peak can be interpreted as an inter-glacial phase that may be headed eventually towards another ice age.
In this paper, the temperature trend in the next 100 years is forecast based on the paleoclimate record using the Simplex Projection Method (SPM). This method has been previously applied on measles, chickenpox and marine phytoplankton data sets to distinguish chaos from environmental noise. A more recent application of the SPM involves the recovery of lost high-frequency components of a bandlimited signal due to undersampling.
Assuming that the SPM accounts for the natural variability of global climate, it may be possible to define the expected range of temperature changes in the next century arising from the chaotic nature of the climate system. This range will enable us to detect the presence of a potential anthropogenic signal or disturbance to the natural behavior of our climate in the future.
[Presented at the Samahang Pisika ng Pilipinas (SPP) Congress, 2000.]