On April 29, 2015, the U.S. Geological Survey (USGS) reported five earthquakes in Oklahoma of magnitude 2.5 or greater—that is, tremors strong enough to be felt. The most powerful of these was a M4.1 earthquake 21 km (13 mi) west of the city of Perry in north-central Oklahoma. Based on recent evidence reported by the USGS, these earthquakes were almost certainly induced by human activity as a consequence of the injection of wastewater from oil and gas production into deep disposal wells. See also: Earthquake; Oil and gas field exploitation; Well

On April 25, 2015 at 11:56 a.m local time, a magnitude 7.8 earthquake struck in the district of Lamjung, approximately 80 km northwest of Kathmandu, Nepal. The earthquake, now known as the Gorkha quake, occurred as the result of thrust faulting [15.0 km (9.3 mi) in depth] in the region where the India plate is sinking (subducting) beneath the Eurasia plate, according to the United States Geological Survey (USGS). Damage to buildings was extensive and over 8700 people were killed. See also: Earthquake; Fault and fault structures; Subduction zones

A magnitude 5.1 nuclear test was detected 376 km (234 mi) NE of Pyongyang, North Korea (DPRK) on January 6, 2015 at 10:30 a.m. local time (01:30 UTC), according to the U.S. Geological Survey (USGS). The event was picked up at seismic stations around the world. The Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) said that the explosion occurred in roughly the same area as North Korea’s previous nuclear test on February 12, 2013. See also: Nuclear explosion; Nuclear testing; Seismographic instrumentation

Wildfires are a natural phenomenon in many ecosystems, including forests along the U.S. Pacific West Coast, as natural fires serve to rejuvenate ecological communities. However, from mid-August through mid-September 2020, forests in California, Oregon, and Washington State suffered through unprecedented wildfires caused by extreme weather events that can be attributed to climate change. By September 15, 2020, in Washington state, 700,000 acres (280,000 hectares) had burned; in Oregon, about 1 million acres (405,000 hectares) had burned; and in California, the worst-hit state, more than 7700 fires had burned 3 million acres (1.2 million hectares), damaged or destroyed more than 5000 structures, and killed at least 35 people. The single largest fire to date was the California Complex fire in Northern California, which was still raging on September 15 after it had already burned about 800,000 acres (320,000 hectares). These epic blazes have created some of the worst air pollution in the world from Seattle, Washington, to Southern California, with haze reaching as far east as New York City. See also: Air pollution; Extreme weather events; Forest fire; Global climate change; Wildfire impact on air quality

Sea-level rise is caused by adding mass (water) and heat to the ocean. The Antarctic ice sheet represents a potentially large source of water. Knowing the speed and direction (velocity) at which the Antarctic ice sheet is flowing to the ocean is important for assessing current and future sea-level rise. Scientists from the University of California, Irvine, and the NASA Jet Propulsion Laboratory have published the most precise map ever of Antarctic ice velocity in the journal Geophysical Research Letters (July 2019). The new map will be useful for mass-balance and ice-thickness studies of the Antarctic ice sheet as well as for modeling climate and sea-level rise. Compared to earlier maps, the new map is 10 times more accurate in terms of ice-flow direction and speed and shows ice movement over 80 percent of Antarctica versus 20 percent shown in past maps. See also: Antarctica; Climate modeling; Glaciology; Global climate change; Sea-level rise

In 1987, the Montreal Protocol, the international treaty banning chemicals that deplete the ozone layer, was adopted. Thirty years later, NASA scientists reported in the journal Geophysical Research Letters (January 2018) satellite measurements showing decreased stratospheric ozone depletion as a result of declining levels of ozone-depleting chlorine from the breakdown of chlorofluorocarbons (CFCs)—that is, chemicals that were used as solvents, refrigerants, and aerosol-can propellants. The ozone hole is an area of severely depleted ozone in the stratosphere over Antacrtica, appearing at the beginning of Southern Hemisphere spring (August–October). From 2005 to 2016, instruments aboard the NASA Aura satellite measured chlorine and ozone levels in the Antarctic ozone hole. As compared to measurements taken in 2005, the measurements showed about a 20 percent decline in ozone depletion during the Antarctic winter. This is the first study to confirm that the ozone hole has begun healing and that the recovery can be attributed to the implementation of the Montreal Protocol. See also: Antarctica; Halogenated hydrocarbon; Ozone; Stratosphere; Stratospheric ozone

A powerful magnitude 7.8 earthquake struck Ecuador on April 16, 2016 at 6:58 p.m. local time, causing extensive damage to buildings and infrastructure as well as hundreds of fatalities and thousands of injuries. The epicenter was located 52.0 km (32.3 mi) west of Rosa Zarate. The earthquake occurred as the result of thrust faulting 19.2 km (11.9 mi) in depth near the boundary of the Nazca and Pacific plates, according to the U.S. Geological Survey (USGS). See also: Earthquake; Fault and fault structures; Subduction zones

To bolster food security in a warming world, engineers are developing a coating that could better protect seeds, such as beans, from drought in semiarid regions. The coating mimics a mucilage-based hydrogel produced naturally by some seeds, such as basil and chia. The hydrogel traps moisture, regulates nutrient retention, and creates an environment around the seed which promotes the growth of beneficial microorganisms. The artificial coating is accordingly tailored to help protect seeds during germination and early seedling growth. In semiarid regions, water stress caused by a lack of available moisture during these sensitive periods of a plant's development is the highest cause of crop loss worldwide. This water stress on agricultural crops in drought-prone, marginal lands is expected to substantially increase in coming decades because of global climate change. See also: Agricultural engineering; Drought; Farm crops; Global climate change; Mucilage; Seed

On August 5, 2018 at 6:46 p.m. local time, a magnitude 6.9 earthquake struck in Pulau Lombok, Indonesia. The earthquake occurred as the result of thrust faulting at a depth of 10.5 km (6.5 mi) in northern Lombok, according to the United States Geological Survey (USGS). A tsunami warning was issued, but was lifted after only small waves were recorded. Early reports stated that 98 people were killed and more than 200 injured, as the earthquake caused many buildings to collapse. Some structures that collapsed had already been damaged one week earlier (June 29, 2018) when a magnitude 6.4 earthquake struck Lombok, killing 17 people and injuring more than 160. Indonesia is located in a very seismically active zone, in which magnitude 5.0 or greater earthquakes were recorded on 17 of 31 days in July 2018. See also: Earthquake; Earthquake engineering; Fault and fault structures; Seismology; Tsunami

Many questions concerning the sustainable production of biofuels have emerged over recent years in terms of land and water use, pollution from fertilizer and pest-control chemicals, greenhouse-gas production, net energy production, and whether enhanced land-use and climate benefits would result from simply planting trees and eschewing biofuels altogether. According to researchers reporting in the Proceedings of the National Academy of Sciences (September 2020), the answer depends, in part, on optimizing land-use policies and bioenergy production systems. Researchers have concluded that sustainable biofuels could make an important contribution toward reducing greenhouse-gas emissions and stabilizing the global climate if we produce bioethanol from biomass sources, such as perennial grasses, that are grown without affecting the carbon already stored in the ecosystem. See also: Biomass; Ethyl alcohol; Global climate change; Greenhouse effect; Land-use planning; Reforestation