I agree with Tony that there are unlikely to be any key indicators that give clear signals of the types of change that you are interested in — at least when looking ahead, all may become clear in retrospect some years after such changes have occurred.
That said, events like the Arab Spring are likely to become more frequent. Weather events happen every year but major droughts and floods are becoming more common and more likely to hit multiple production regions at the same time.
The effects of climate change on the food supply exacerbated the underlying tensions that have led to ongoing Middle East instability
In 2010, droughts in Russia, Ukraine, China and Argentina and torrential storms in Canada, Australia and Brazil — all major wheat and grain producers — considerably diminished global crops, driving commodity prices up. The region was already dealing with internal sociopolitical, economic and climatic tensions, and the 2010 global food crisis helped drive it over the edge.
But the issue here is much bigger. Because of globalization, regional climate events can have a global extent, the report says. What's more, scenarios where weather events unfold economic and political shifts are likely to be repeated as climate volatility, expanding populations and competition for resources disturb national stability, the report says.
With regard to the phytoplankton matter you raise, I can give some insights. The concern relates to a paper by Boyce et al. (2010) in Nature that indicated a rapid decline in global phytoplankton. The key point being:
since 1899. We observe declines in eight out of ten ocean regions, and estimate a global rate of decline of ~1% of the global median per year.
In science, when you reach a remarkable conclusion, there are going to be many people checking your findings. The following year, McQuatters-Gollop et al. (2011) published findings, also in Nature, questioning Boyce et al.:
Phytoplankton account for approximately 50% of global primary production, form the trophic base of nearly all marine ecosystems, are fundamental in trophic energy transfer and have key roles in climate regulation, carbon sequestration and oxygen production. Boyce et al.1 compiled a chlorophyll index by combining in situ chlorophyll and Secchi disk depth measurements that spanned a more than 100-year time period and showed a decrease in marine phytoplankton biomass of approximately 1% of the global median per year over the past century. Eight decades of data on phytoplankton biomass collected in the North Atlantic by the Continuous Plankton Recorder (CPR) survey2, however, show an increase in an index of chlorophyll (Phytoplankton Colour Index) in both the Northeast and Northwest Atlantic basins3, 4, 5, 6, 7 (Fig. 1), and other long-term time series, including the Hawaii Ocean Time-series (HOT)8, the Bermuda Atlantic Time Series (BATS)8 and the California Cooperative Oceanic Fisheries Investigations (CalCOFI)9 also indicate increased phytoplankton biomass over the last 20–50 years. These findings, which were not discussed by Boyce et al.1, are not in accordance with their conclusions and illustrate the importance of using consistent observations when estimating long-term trends.
In the back and forth of scientific 'discussion' several other authors raised questions of whether the methodology or the analyses methods of Boyce et al. were causing there results to come out so extreme. For example, the older data are from Secchi disks (white disks lowered in the water) which do show the chlorophyll content somewhat but are also registering all other particulates in the water. This makes the early year values seem very high and then when newer methods are used in more recent years that only measure chlorophyll, it looks like a declining trend.
Well, Boyce et al. (2014) have responded last month with a new study that has tried to account for the various criticisms raised since their earlier paper.
After correcting for various factors and testing various methodologies of analysis, they still find a statistically significant trend downward in phytoplankton for 60% of locations, but a statistically significant increase in phytoplankton at 40% of locations. Their conclusions are substantially watered down from those reported in the the initial Nature paper.
We conclude that average upper ocean chlorophyll concentra-tions have declined over the past century but that the absolutemagnitude of this change remains uncertain (global averages fromlocal and regional models were both negative, but varied by a fac-
tor of 7).
The formatting is getting corrupted so I will end this before losing everything a second time! In short, phytoplankton amounts may be declining slightly but this is not happening at a catastrophic rate. The greatest declines are seen far from the continental shelves. Areas with increases counteract much of the areas of decreases.