There's a concern that global warming may push Earth's climate system past a "tipping point," where rapid melting of ice and further warming may become irreversible. It's a hotly debated conjecture because there is no picture of what this point of no return may look like.

To try and find some answers about the future, researchers have probed the geologic past and drawn some conclusions about mechanisms of abrupt climate change. The study pinpoints the emergence of synchronized climate variability in the North Pacific Ocean and the North Atlantic Ocean a few hundred years before the rapid warming that took place at the end of the last ice age about 15,000 years ago.

It sounds like it should be easy enough to know if ice is growing or retreating, but it really isn't.  Antarctic sea ice has been expanding, we are told, while Arctic sea ice is retreating, both at dramatic rates.

How accurate is satellite data? Processing errors can be a problem, but they are more heavily scrutinized whenever a study finds that sea ice anywhere is increasing. A paper in The Cryosphere tackles the satellite data problem, for the increase measured in Southern Hemisphere sea ice.

A new study indicates sea levels likely will continue to rise in the tropical Pacific Ocean off the coasts of the Philippines and northeastern Australia as humans continue to alter the climate.

The study authors combined past sea level data gathered from both satellite altimeters and traditional tide gauges to find out how much a naturally occurring climate phenomenon called the Pacific Decadal Oscillation, or PDO, influences sea rise patterns in the Pacific.

As sea ice begins to melt back toward its late September minimum, it is being watched by researchers who have put sensors on and under ice in the Beaufort Sea. 

The international effort hopes to figure out the physics of the ice edge in order to better understand and predict open water in Arctic seas.

"This has never been done at this level, over such a large area and for such a long period of time," said principal investigator Craig Lee, an oceanographer at the University of Washington's Applied Physics Laboratory. "We're really trying to resolve the physics over the course of an entire melt season."

A new study on biological erosion of mesophotic tropical coral reefs - low energy reef environments between 30-150 meters deep - provides new insights into processes that affect the overall structure of these important ecosystems.

The purpose of the study was to better understand how bioerosion rates and distribution of bioeroding organisms, such as fish, mollusks and sponges, differ between mesophotic reefs and their shallow-water counterparts and the implications of those variations on the sustainability of the reef structure.

Changes to Antarctic winds have been implicated in southern Australia's drying climate but a new estimate says they may also have a profound impact on warming ocean temperatures under the ice shelves along the coastline of West and East Antarctic.

Whales are relatively rare and so they probably don't make much of a difference in the overall ocean. 

A team of biologists disagrees. They reviewed several decades of research on whales from around the world and found that whales make a huge difference and have a powerful and positive influence on the function of oceans, global carbon storage, and the health of commercial fisheries. "The decline in great whale numbers, estimated to be at least 66% and perhaps as high as 90%, has likely altered the structure and function of the oceans," claims University of Vermont conservationist Joe Roman and colleagues in Frontiers in Ecology and the Environment, "but recovery is possible and in many cases is already underway."

Iron is one of the essential elements of life. Found in enzymes like myoglobin and hemoglobin and cytochrome P450, iron is an essential cog in the biomachinery of every living cell. 

Iron is present in tiny concentrations in seawater. On the order of a few billionths of a gram in a liter.  Given that there is so little iron in seawater, one might conclude that its presence there is inconsequential, but its scarcity in the ocean, the earth's wellspring of life, only magnifies its importance. 

A paper in Scientific Reports posits a new cause of the ice age that covered large parts of the Northern Hemisphere 2.6 million years ago.

The study found a previously unknown mechanism by which the joining of North and South America changed the salinity of the Pacific Ocean and caused major ice sheet growth across the Northern Hemisphere. The change in salinity encouraged sea ice to form which in turn created a change in wind patterns, leading to intensified monsoons. These provided moisture that caused an increase in snowfall and the growth of major ice sheets, some of which reached over a mile in thickness.

If your glass is half full, you recognize that in recent geological history, 90,000 of every 100,000 years have been ice ages, and it's been 12,000 years since the last one. In that light, global warming might be a good thing.