  Determining whether Global Average Temperature (GAT) is an integrated process
of order 1, I(1), or is a stationary process around a trend function is crucial
for detection, attribution, impact and forecasting studies of climate change.
In this paper, we investigate the nature of trends in GAT building on the
analysis of individual temperature grids. Our 'micro-founded' evidence suggests
that GAT is stationary around a non-linear deterministic trend in the form of a
linear function with a one-period structural break. This break can be
attributed to a combination of individual grid breaks and the standard
aggregation method under acceleration in global warming. We illustrate our
findings using simulations.
