  The progress article - Widening of the tropical belt in a changing climate -
by Seidel et al. (2008) published in the first issue of Nature Geosciences,
summarizes the results of several methods to determine the width of the
tropical zone. All they show evidence that the tropics have been expanding over
the past few decades. We confirm this widening based on one more indicator -
the position of the subtropical centers of high pressure. However, we question
the implication of the authors that the tropics widen in response to human
activity, and suggest as a more probable cause the increasing solar activity.
Consequently, we question their conclusion that this widening may continue into
the future in association with anthropogenic climate change, and suggest that
whether the tropics will continue widening will depend on the future evolution
of solar activity rather than on anthropogenic activity.
