A new effort to reconstruct Earth’s climate since the last ice age, about 24,000 years ago, highlights the main drivers of climate change, and how far out of bounds human activity has pushed the climate system.

The University of Arizona-led study uses a technique for reconstructing past temperatures developed by co-authors at the 91̽��. The , published Nov. 10 in Nature, has three main findings:

• It verifies that the main drivers of climate change since the last ice age are rising greenhouse gas concentrations and the retreat of the ice sheets
• It suggests a general warming trend over the last 10,000 years — settling a decade-long debate in the paleoclimatology community about whether this period trended warmer or cooler
• The magnitude and rate of warming over the last 150 years far surpasses the magnitude and rate of changes at any other time over the last 24,000 years

“This reconstruction suggests that current temperatures are unprecedented in 24,000 years, and also suggests that the speed of human-caused global warming is faster than anything we’ve seen in that same time,” said senior author , an associate professor at the University of Arizona.

The 91̽��team developed the method that allowed researchers to use computers to make sense of the paleoclimate data in marine sediments, allowing for more regional detail and precision in the temperature history.

“The fact that we’re today so far out of bounds of what we might consider normal is cause for alarm and should be surprising to everybody,” said lead study author , a postdoctoral researcher at the University of Arizona.

An online search of “global temperature change since the last ice age” would produce a graph of global temperature change over time that was .

“Our team’s reconstruction improves on that curve by adding a spatial dimension,” Tierney said.

Different methods exist for reconstructing past temperatures. The team combined two independent datasets – temperature data from marine sediments and computer simulations of climate – to create a more complete picture of the past.

“Paleoclimate records provide the only record we have of these past climates, but these records are imperfect and they have gaps in space and time. Climate models provide simulations based on the laws of physics, but lack the observational record,” said co-author , a 91̽��professor of atmospheric sciences. “Combining models and paleoclimate proxies — using the technique we developed for the — provides the best spatially complete estimate of the actual past climate, constrained by physics.”

The researchers looked at the chemical signatures of marine sediments to get information about past temperatures. Because temperature changes over time can affect the chemistry of a long-dead animal’s shell, paleoclimatologists can use those measurements to estimate temperature in an area. It’s not a perfect thermometer, but it’s a starting point.

Computer-simulated climate models, on the other hand, provide temperature information based on scientists’ best understanding of the physics of the climate system, which also isn’t perfect.

The team decided to combine the methods to harness the strengths of each. This is called data assimilation and is also commonly used in weather forecasting.

“To forecast the weather, meteorologists start with a model that reflects current weather, then add in observations such as temperature, pressure, humidity, wind direction and so on to create an updated forecast,” Tierney said.

The team applied this same idea to past climate.

“We found remarkable agreement between the output from our assimilation method and the values in independent paleoclimate records,” Hakim said. “This independent validation of our estimates for the past climate variability is an indication of how much the results can be trusted.”

The other co-authors are at the UW; Jiang Zhu at the National Center for Atmospheric Research; Jonathan King at the University of Arizona; and Christopher Poulsen at the University of Michigan. The research was funded by the National Science Foundation, the Heising-Simons Foundation, and the National Center for Atmospheric Research.

For more information, contact Hakim at ghakim@uw.edu, Osman at mattosman@arizona.edu and Tierney at jesst@arizona.edu.

Note: This article was adapted from a UArizona .

NSF grants: AGS-1602301, AGS-1602223; HSF grants: 2016-012, 2016-014, 2016-015

Humans have always been frightened and fascinated by lightning. This month, NASA is scheduled to launch a new satellite that will provide the first nonstop, high-tech eye on lightning over the North American section of the planet.

91̽�� researchers have been tracking global lightning from the ground for more than a decade. Lightning is not only about public safety — lightning strike information has recently been introduced into weather prediction, and a 91̽��study shows ways to apply it in storm forecasts.

“When you see lots of lightning you know where the convection, or heat-driven upward motion, is the strongest, and that’s where the storm is the most intense,” said co-author , a 91̽��professor of Earth and space sciences. “Almost all lightning occurs in clouds that have ice, and where there’s a strong updraft.”

The recent , published in the American Meteorological Society’s Journal of Atmospheric and Oceanic Technology, presents a new way to transform lightning strikes into weather-relevant information. The U.S. National Weather Service has begun to use lightning in its most sophisticated forecasts. This method, however, is more general and could be used in a wide variety of forecasting systems, anywhere in the world.

The authors tested their method on two cases: the summer 2012 thunderstorm system that swept across the U.S., and a 2013 that killed several people in the Midwest.

“Using lightning data to modify the air moisture was enough to dramatically improve the short-term forecast for a strong rain, wind and storm event,” said first author , a former 91̽��graduate student who now works for The Weather Company. His simple method might also improve medium-range forecasts, for more than a few days out, in parts of the world that have little or no ground-level observations.

The study used data from the UW-based , which has a global record of lightning strikes going back to 2004. Director Holzworth is a plasma physicist who is interested in what happens in the outer edges of the atmosphere. But the network also sells its data to commercial and government agencies, and works with scientists at the 91̽��and elsewhere.

A few years ago Holzworth joined forces with colleagues in the 91̽��Department of Atmospheric Sciences to use lightning to improve forecasts for convective storms, the big storms that produce thunderstorms and tornadoes.

Apart from ground stations, weather forecasts are heavily dependent on weather satellites for information to start or “initialize” the numerical weather prediction models that are the foundation of modern weather prediction.

What’s missing is accurate, real-time information about air moisture content, temperature and wind speed in places where there are no ground stations.

“We have less skill for thunderstorms than for almost any other meteorological phenomenon,” said co-author , a 91̽��professor of atmospheric sciences. “This paper shows the promise of lightning information. The results show that lightning data has potential to improve high-resolution forecasts of thunderstorms and convection.”

The new method could be helpful in forecasting storms over the ocean, where no ground instruments exist. Better knowledge of lightning-heavy tropical ocean storms could also improve weather forecasts far from the equator, Mass said, since many global weather systems originate in the tropics.

The study was funded by NASA and the National Oceanic and Atmospheric Administration. , a 91̽��professor of atmospheric sciences, is the other co-author.

The UW-based Worldwide Lightning Location Network began in 2003 with 25 detection sites. It now includes some 80 at universities or government institutions around the world, from Finland to Antarctica.

The latest thinking on how lightning occurs is that ice particles within clouds separate into lighter and heavier pieces, and this creates charged regions within the cloud. If strong updrafts of wind make that altitude separation big enough, an electric current flows to cancel out the difference in charges.

A bolt of lightning creates an electromagnetic pulse that can travel a quarter way around the planet in a fraction of a second. Each lightning network site hosts an 8- to 12-foot antenna that registers frequencies in the 10 kilohertz band, and sends that information to a sound card on an Internet-connected laptop. When at least five stations record a pulse, computers at the 91̽��register a lightning strike, and then triangulate the arrival times at different stations to pinpoint the location.

The network’s shows lightning strikes for the most recent 30 minutes in Google Earth. An alternate shows the last 40 minutes of lightning in different parts of the world on top of NASA cloud maps, which are updated from satellites every 30 minutes. The program is the longest-running real-time global lightning location network, and it is operated by the research community as a global collaboration.

Lightning already kills hundreds of people every year. That threat may be growing — a recent study projected that lightning will become with climate change.

“The jury’s still out on any long-term changes until we have more data,” Holzworth said. “But there is anecdotal evidence that we’re seeing lightning strikes in places where people are not expecting it, which makes it more deadly.”

On Nov. 19, NASA is scheduled to launch the new satellite that will be the first geostationary satellite to include an to continuously watch for lightning pulses. Holzworth will help calibrate the new instrument, which uses brightness to identify lightning, against network data. NASA also funded the recent research as one of the potential applications for lightning observations.

“GOES-R will offer more precise, complete lightning observations over North and South America, which will supplement our global data,” Holzworth said. “This launch has been long anticipated in the lightning research community. It has the potential to improve our understanding of lightning, both as a hazard and as a forecasting tool.”

###

For more information, contact Holzworth at 206-685-7410 or bobholz@uw.edu, Mass at 206-685-0910 or cmass@uw.edu and Dixon at ken.dixon@weather.com.

“With this approach we could potentially have tens or hundreds of thousands of additional surface pressure observations, which could significantly improve short-term weather forecasts,” said , a 91̽��professor of atmospheric sciences.

Owners of certain new Android smartphones and tablet computers can now download the app, which measures atmospheric pressure and provides the data to 91̽��researchers.

When some smartphone manufacturers recently added pressure sensors, to estimate the phone’s elevation and help pinpoint its location, Mass saw an opportunity to enhance weather prediction. In the autumn he approached , a Canadian app company that developed a barometer application for smartphones that collects all the data and shares it back with users.

The PressureNet app this week collected about 4,000 observations per hour, with users clustered in the northeastern United States and around some major cities.

“We need more density,” Mass said. “Right now it’s a matter of getting more people to contribute.”

Android devices equipped with pressure sensors include Samsung’s Galaxy S3, Galaxy Nexus, Galaxy Note and Nexus 4 smartphones, and the Nexus 10 and Motorola Xoom tablet computers.

Atmospheric pressure is the weight of the air above, and includes information about what is happening as air masses collide. Precise tracking of pressure readings and pressure changes could help weather forecasters to pinpoint exactly where and when a major storm will strike.

Mass is particularly interested in the center of the country, which is prone to severe storms but includes fewer weather observation stations.

“Thunderstorms are one of the areas of weakest skill for forecasting,” Mass said. “I think thunderstorms in the middle part of the country could potentially be the biggest positive for this approach. They are relatively small-scale, they develop over a few hours, they can be severe and can affect people significantly.”

Tracking storms a few hours out could help people better protect themselves and their property. In the Seattle area, the tool could improve short-term forecasts for wind and rain.

“I think this could be one of the next major revolutions in weather forecasting, really enhancing our ability to forecast at zero to four hours,” Mass said.

Cumulonimbus updated the app’s privacy settings last week so users could allow access to the data by scientific researchers. Since then, the 91̽��group has been uploading the pressure data each hour and preparing it for use in weather forecasting models. The data will soon be available to all researchers who want to incorporate it in weather-prediction tools.

A project begun in 2010 by Mass and , a 91̽��professor of atmospheric sciences, has explored ways to improve weather forecasts by taking advantage of surface pressure measurements. The current network of U.S. weather stations offers about one thousand air-pressure readings. Adding observations collected by small-scale weather networks and hobbyists, the 91̽��team found, improves the forecasts. A weather station in every pocket would offer an unprecedented wealth of data.

A recent by Mass explains more about the 91̽��group’s approach. , a 91̽��graduate student in atmospheric sciences, will load the smartphone data into a weather-forecasting system. At first the tool will use only stationary data points, but eventually it may include data from devices in motion.

Building the system will take a few months, Mass said. By this summer’s thunderstorm season he hopes the 91̽��team will be using smartphone data to forecast storms and compare their results against traditional forecasts.

If the technique is successful, the researchers hope to supply it to the National Weather Service and the weather bureaus of other countries.

The technique could be particularly useful, Mass noted, in countries that have little weather-forecasting infrastructure but where smartphones are becoming more common.

The research has been funded by Microsoft Corp. and the National Weather Service.

###

For more information, contact Mass at 206-685-0910 or cliff@atmos.washington.edu.

The next colloquium in the MathAcrossCampus series will be Estimation and Prediction of Complex Systems: Progress in Weather and Climate, to be presented by Greg Hakim, 91̽��associate professor of atmospheric sciences.

The talk will be held from 4 to 5 p.m. Thursday, Dec. 3, in 210 Kane, and will be followed by a reception.

MathAcrossCampus is a quarterly colloquium series designed to expose students and researchers to a wide variety of applications of mathematics to real-world problems, with a special emphasis on the growing role of discrete methods in math applications.

The series consists of on main talk each quarter, followed by a reception, as well as a separate discussion with each speaker.