A new study has claimed that it is harder than experts thought to predict when sudden shifts in earth's natural systems will occur. Researchers at University of California, Davis, said many scientists are looking for the warning signs that herald sudden changes in natural systems, in hopes of forestalling those changes or improving our preparations for them.The study, however says that unfortunately the regime shifts with potentially large consequences can happen without warning. It further says that some effects of global climate change on ecosystems can be seen only once the effects are dramatic.The report adds that by that point returning the system to a desirable state will be difficult, if not impossible."