Predicting the potential effects of climate change on crop yields requires a model of how crops respond to weather. As predictions from different models often disagree, understanding the sources of this divergence is central to building a more robust picture of climate change's likely impacts. A common approach is to use statistical models trained on historical yields and some simplified measurements of weather, such as growing season average temperature and precipitation. Although the general strengths and weaknesses of statistical models are widely understood, there has been little systematic evaluation of their performance relative to other methods. Here we use a perfect model approach to examine the ability of statistical models to predict yield responses to changes in mean temperature and precipitation, as simulated by a process-based crop model. The CERES-Maize model was first used to simulate historical maize yield variability at nearly 200 sites in Sub-Saharan Africa, as well as the impacts of hypothetical future scenarios of 2◦C warming and 20% precipitation reduction. Statistical models of three types (time series, panel, and cross-sectional models) were then trained on the simulated historical variability and used to predict the responses to the future climate changes. The agreement between the process-based and statistical models' predictions was then assessed as a measure of how well statistical models can capture crop responses to warming or precipitation changes. The performance of statistical models differed by climate variable and spatial scale, with time-series statistical models ably reproducing site-specific yield response to precipitation change, but performing less well for temperature responses. In contrast, statistical models that relied on information from multiple sites, namely panel and cross-sectional models, were better at predicting responses to temperature change than precipitation change. The models based on multiple sites were also much less sensitive to the length of historical period used for training. For all three statistical approaches, the performance improved when individual sites were first aggregated to country-level averages. Results suggest that statistical models, as compared to CERES-Maize, represent a useful if imperfect tool for projecting future yield responses, with their usefulness higher at broader spatial scales. It is also at these broader scales that climate projections are most available and reliable, and therefore statistical models are likely to continue to play an important role in anticipating future impacts of climate change.

Condoleezza Rice has excelled as a diplomat, political scientist, and concert pianist.  Her achievements run the gamut from helping to oversee the collapse of communism in Europe and the decline of the Soviet Union, to working to protect the country in the aftermath of 9-11, to becoming only the second woman - and the first black woman ever -- to serve as Secretary of State.
 
But until she was 25 she never learned to swim.
 
Not because she wouldn't have loved to, but because when she was a little girl in Birmingham, Alabama, Commissioner of Public Safety Bull Connor decided he'd rather shut down the city's pools than give black citizens access.
 
Throughout the 1950's, Birmingham's black middle class largely succeeded in insulating their children from the most corrosive effects of racism, providing multiple support systems to ensure the next generation would live better than the last.  But by 1963, when Rice was applying herself to her fourth grader's lessons, the situation had grown intolerable.  Birmingham was an environment where blacks were expected to keep their head down and do what they were told -- or face violent consequences. That spring two bombs exploded in Rice's neighborhood amid a series of chilling Klu Klux Klan attacks.  Months later, four young girls lost their lives in a particularly vicious bombing.
 
So how was Rice able to achieve what she ultimately did?
 
Her father, John, a minister and educator, instilled a love of sports and politics.  Her mother, a teacher, developed Condoleezza's passion for piano and exposed her to the fine arts.  From both, Rice learned the value of faith in the face of hardship and the importance of giving back to the community.  Her parents' fierce unwillingness to set limits propelled her to the venerable halls of Stanford University, where she quickly rose through the ranks to become the university's second-in-command.  An expert in Soviet and Eastern European Affairs, she played a leading role in U.S. policy as the Iron Curtain fell and the Soviet Union disintegrated.  Less than a decade later, at the apex of the hotly contested 2000 presidential election, she received the exciting news - just shortly before her father's death - that she would go on to the White House as the first female National Security Advisor. 
 
As comfortable describing lighthearted family moments as she is recalling the poignancy of her mother's cancer battle and the heady challenge of going toe-to-toe with Soviet leaders, Rice holds nothing back in this remarkably candid telling. This is the story of Condoleezza Rice that has never been told, not that of an ultra-accomplished world leader, but of a little girl - and a young woman -- trying to find her place in a sometimes hostile world and of two exceptional parents, and an extended family and community, that made all the difference.