Scientists have warned that severe drought and precipitation are among the risks of greenhouse-gas-induced climate change, but a study published in the journal Nature finds that extremely warm temperatures do not always translate into record wet and dry extremes. Highlighting the complexities in predicting the effects of planetary warming on precipitation, lead author Fredrik Ljungqvist of Stockholm University said that more dramatic wet-dry weather extremes had occurred in centuries cooler than the 20th century.
"Several other centuries show stronger and more widespread extremes," he said. "We can't say it's more extreme now."
In this first hemispheric-scale, centuries-long water availability assessment, the researchers statistically analyzed evidence for changes in precipitation and drought, compiling hundreds of precipitation records across the Northern Hemisphere from historical accounts as well as archives on such things as tree-rings and lake sediments.
They detected a pattern of alternating moisture regimes throughout the last 12 centuries, suggesting that "the instrumental period is too short to capture the full range of natural hydroclimate variability."
Their finding that the last century's temperature rise may not have affected the hydroclimate as much as previously thought challenges the conclusions of the United Nations Intergovernmental Panel on Climate Change.
In a News and Views article published in Nature, Matthew Kirby of California State University at Fullerton suggested that current climate models should not be discarded because their results, which indicate that "dry gets dryer and wet gets wetter," do not match the Ljungqvist team's proxy results, which indicate no difference in the water dynamics of the 20th century and those of the pre-industrial era.
"Do their results invalidate current predictive models?" Kirby asked. "Certainly not. But they do highlight a big challenge for climate modellers, and present major research opportunities both for modellers and for climate scientists who work with proxy data."
Study: Climate Change Causing Earth to Shift
A study published in the journal Science Advances reveals that climate change affects how Earth tilts on its axis. Although scientists have known that Earth's spin axis has been drifting due to ice cap melt in Greenland and Antarctica, the new research suggests that changes in terrestrial water storage also play a role in the planet's decadal axis swings. The finding is based on data collected from NASA's Gravity Recovery and Climate Experiment (GRACE) satellite, which can detect changes in the mass of Earth's ice sheets and oceans.
Before 2000, Earth's spin axis was moving westward toward Canada, but since then, climate-change-driven ice loss has pulled the direction of drift eastward approximately seven inches a year--a shift that lead researcher Surendra Adhikari of NASA's Jet Propulsion Laboratory described as "very dramatic" and that scientists say is meaningful.
"This is the first time we have solid evidence that changes in land water distribution on a global scale also shift which direction the axis moves to," said Adhikari.
Although the study data doesn't indicate whether the most recent shift in the pole is the result of human activities, the study authors think they will be able to use them to tease out man-made climate change later this year. Because polar motion and climate variability appear to be linked, scientists can examine historical records of the pole's motion in relation to changes in Earth's climate. If those changes are less dramatic than the ones evidenced today, scientists could assert that global warming has a controlling influence on Earth's poles.
U.N. Climate Agreement Terms Studied, Launch Pegged Early
Next week on Earth Day (April 22), 130 countries are expected to sign the Paris Climate Agreement, which has a goal of limiting average surface temperatures to "well below" 2 degrees Celsius. But already the United Nations Intergovernmental Panel on Climate Change is looking into the feasibility of what U.N. Climate Chief Christiana Figueres describes as "a moonshot": limiting global emissions to 1.5 degrees Celsius.
Figueres believes the Paris agreement will take effect in 2018--two years sooner than currently slated.
The agreement will come into force once 55 parties representing 55 percent of the world's total emissions have both signed and ratified it.
The Climate Post offers a rundown of the week in climate and energy news. It is produced each Thursday by Duke University's Nicholas Institute for Environmental Policy Solutions.