  In many scientific fields, such as economics and neuroscience, we are often
faced with nonstationary time series, and concerned with both finding causal
relations and forecasting the values of variables of interest, both of which
are particularly challenging in such nonstationary environments. In this paper,
we study causal discovery and forecasting for nonstationary time series. By
exploiting a particular type of state-space model to represent the processes,
we show that nonstationarity helps to identify causal structure and that
forecasting naturally benefits from learned causal knowledge. Specifically, we
allow changes in both causal strengths and noise variances in the nonlinear
state-space models, which, interestingly, renders both the causal structure and
model parameters identifiable. Given the causal model, we treat forecasting as
a problem in Bayesian inference in the causal model, which exploits the
time-varying property of the data and adapts to new observations in a
principled manner. Experimental results on synthetic and real-world data sets
demonstrate the efficacy of the proposed methods.
