JOHN: TONIGHT ON PBS NEWS WEEKEND.

DESPITE A COURT ORDER, HUNDREDS OF VENEZUELANS ARE DEPORTED TO EL SALVADOR UNDER A RARELY USED 18TH CENTURY LAW.

THEN, THE DOGE LAYOFFS AT THE FAA AND WHAT THEY COULD MEAN FOR AVIATION SAFETY.

AND AFTER A WEEK OF CLIMATE CHANGE ROLLBACKS AT THE EPA, THE EVIDENCE OF RISING GLOBAL TEMPERATURES THAT IS ALARMING SCIENTISTS.

MICHAEL: WE ARE ALREADY SEEING TRULY DANGEROUS CLIMATE CONSEQUENCES AND THEY WILL JUST GET MORE AND MORE DANGEROUS IF WE CONTINUE DOWN THIS ROAD.

♪ JOHN: GOOD EVENING, I'M JOHN YANG.

NEARLY 300 VENEZUELANS ARE IN EL SALVADOR TONIGHT, DEPORTED FROM - - AFTER BEING DEPORTED FROM THE UNITED STATES WITHOUT A HEARING UNDER A RARELY USED 18TH CENTURY LAW AND DESPITE A FEDERAL JUDGE'S ORDER BLOCKING THE MOVE.

THIS MORNING, EL SALVADOR PRESIDENT NAYIB BUKELE POSTED VIDEO ON TWITTER SHOWING THEM ARRIVING AND BEING TAKEN INTO CUSTODY.

THE TRUMP ADMINISTRATION SAYS THEY ARE MEMBERS OF A NOTORIOUS VENEZUELAN GANG CALLED TREN DE ARAGUA AND SUMMARILY DEPORTED THEM UNDER THE ALIEN ENEMIES ACT OF 1798.

THEY LANDED IN EL SALVADOR JUST HOURS AFTER A FEDERAL JUDGE BLOCKED THE ADMINISTRATION FROM USING THAT LAW TO DEPORT ANYONE AND ORDERED ANY PLANES THAT HAD TAKEN OFF TO TURN AROUND.

KATHERINE YON EBRIGHT IS A COUNSEL AT THE BRENNAN CENTER FOR JUSTICE.

WHAT DO YOU MAKE OF THAT?

THE JUDGE SAID THE PLANES HAD TO TURN AROUND AND CLEARLY THEY DID NOT ALL STOP KATHERINE: IT IS A REAL CHALLENGE FOR THE RULE OF LAW, OUR SYSTEMS OF CHECKS AND BALANCES.

PART OF THIS IS THAT THIS IS A DISTRICT COURT, NOT A COURT OF APPEALS, AND I SHOULD HOPE THAT AS THIS CASE PROGRESSES AS WE MOVE PAST THE TEMPORARY RESTRAINING ORDER OR THE JUDGE'S ORDER IN THIS CASE AT THIS TIME THAT THE FEDERAL GOVERNMENT'S COMPLIANCE WITH THE COURT'S ORDERS BECOMES SERIOUS AND AND ROBUST.

AGAIN, CONSISTENT WITH OUR SYSTEM OF CHECKS AND BALANCES.

JOHN: WHAT IS THE ALIEN ENEMIES ACT OF 1798, AND HOW HAS IT BEEN USED IN THE PAST?

KATHERINE: THE ALIEN ENEMIES ACT IS A WARTIME AUTHORITY.

IT IS NOT AN IMMIGRATION AUTHORITY, PARTICULARLY NOT IN PEACETIME.

IT ALLOWS THE PRESIDENT, WHEN THERE'S A DECLARED WAR, AN INVASION OR PREDATORY INCURSION.

THOSE ARE ACTS OF WAR, TO REGULATE, DETAIN AND DEPORT INDIVIDUALS WHO DO NOT HAVE U.S.

CITIZENSHIP WHO ARE FROM THE COUNTRY WITH WHICH WE'RE AT WAR, AND CONSISTENT WITH THIS BEING A WARTIME AUTHORITY, IT'S ONLY BEEN USED IN 3 CONFLICTS, THE WAR OF 1 12, WORLD WAR I AND WORLD WAR II.

REVIVING THIS KIND OF LAW PARTICULARLY AGAIN FOR PEACETIME IMMIGRATION ENFORCEMENT IS WILDLY INAPPROPRIATE.

JOHN: UNDER A DECLARED WAR OR INVASION.

NOW PRESIDENT TRUMP AND HIS EXECUTIVE ORDER JUSTIFIED USING THIS LAW BY SAYING THAT THESE GANG MEMBERS HAVE UNLAWFULLY INFILTRATED THE UNITED STATES AND ARE CONDUCTING IRREGULAR WARFARE AND UNDERTAKING HOSTILE ACTIONS AGAINST THE UNITED STATES.

IN YOUR VIEW, IS THAT ENOUGH TO USE THIS LAW?

KATHERINE: THAT'S TRUMPED UP RHETORIC.

WHAT WE ARE SEEING FROM THE GANG TO THE EXTENT THAT IT IS IN THE UNITED STATES IS CRIMINAL ACTIVITY AND CERTAINLY CRIMINAL ACTIVITY SHOULD BE TAKEN SERIOUSLY, AND INDIVIDUALS WHO ARE MEMBERS OF THIS GANG OR INDIVIDUALS WHO ARE COMMITTING SERIOUS CRIMES IN THE UNITED STATES CAN BE DETAINED AND THEN DEPORTED UNDER PEACETIME IMMIGRATION LAW.

YOU DO NOT NEED TO TURN TO A WARTIME AUTHORITY FROM 1798 LAST USED FOR INTERNMENT IN WORLD WAR II TO ADDRESS CRIMINAL ACTIVITY OR UNLAWFUL MIGRATION.

AND I WILL SAY THAT THE PROCLAMATION THAT THE PRESIDENT ISSUED DOES COVER PEOPLE WHO ARE LAWFULLY PRESENT IN THE UNITED STATES, AND SO YOU CAN'T SAY THAT INVOKING THE ALIEN ENEMIES ACT IS ACTUALLY ABOUT UNLAWFUL MIGRATION.

WHILE SAYING THAT WE'RE GOING TO TARGET PEOPLE WHO ARE HERE LAWFULLY.

JOHN: LAST NIGHT, THE ATTORNEY GENERAL PAM BONDI SAID THAT THE COURT ORDER PUTS THE PUBLIC AND LAW ENFORCEMENT AT RISK.

WHAT DO YOU SAY TO THAT?

KATHERINE: THE WAY THAT THE COURT ORDER WAS ANNOUNCED AND WRITTEN, IS IT ONLY APPLIES TO INDIVIDUALS WHO ARE IN CUSTODY ALREADY.

AND SO, WHAT RISK IS POSED BY PEOPLE WHO ARE ALREADY DETAINED FOR HAVING UNDERTAKEN CRIMINAL ACTIVITY OR BEING SUSPECTED OF A GANG MEMBERSHIP, AND SO THERE'S NO WAY, SHAPE OR FORM IN WHICH THERE IS AN IMMINENT OR ONGOING PUBLIC SAFETY OR NATIONAL SECURITY RISK THAT EMANATES FROM THE ORDER THAT THE JUDGE ISSUED.

JOHN: WHAT COULD THE ACLU DO ABOUT THE VENEZUELANS WHO LANDED IN EL SALVADOR, DESPITE THE THE JUDGE'S ORDER.

IS THERE ANYTHING, ANY RECOURSE?

KATHERINE: THE JUDGE WAS QUITE CLEAR THAT ONCE INDIVIDUALS ARE IN EL SALVADOR, THEY FALL BEYOND THE COURT'S JURISDICTION.

I THINK ACLU CAN AND SHOULD RAISE WITH THE JUDGE THE NONCOMPLIANCE, HOWEVER, WITH THE JUDGE'S ORDER AND SEE WHAT AVENUES ARE AVAILABLE TO TRY TO ENSURE THAT THE GOVERNMENT DOES COMPLY WITH FUTURE ORDERS, INCLUDING, YOU KNOW, COMPLY WITH THE ORDER THAT'S ALREADY ON THE BOOKS.

JOHN: WHAT DO YOU THINK THE SIGNIFICANCE, THE LARGER SIGNIFICANCE IS OF THE PRESIDENT INVOKING THIS ACT.

KATHERINE: AS I'VE SAID, IT'S A WARTIME AUTHORITY.

IT CANNOT, SHOULD NOT BE USED FOR PEACETIME IMMIGRATION ENFORCEMENT.

I THINK ON THE GROUND THERE ARE VENEZUELAN IMMIGRANT COMMUNITIES.

THERE ARE U.S. CITIZENS OF VENEZUELAN DESCENT WHO ARE WORRIED THAT THEY'RE GOING TO BE TARGETED, WRONGLY ACCUSED OF BEING MEMBERS OF TRENDE ARAGUA .

DEPORTED WITHOUT EVIDENCE, WITHOUT A HEARING, AND THAT'S THE KIND OF THING THAT IS FRANKLY UN-AMERICAN.

TARGETING PEOPLE WITHOUT THEIR RIGHTS BASED ON WHERE THEY WERE BORN, WHAT THEY LOOK LIKE, AND YET THAT IS THE MOMENT THAT WE'RE IN, AND MY HOPE IS THAT THE COURTS SHUT THIS DOWN PROMPTLY.

BECAUSE NOT ONLY IS THIS AN ABUSE OF A LAW, THIS IS A USE OF IT THAT DOES NOT SQUARE WITH THE TEXT OR THE HISTORY OF THE LAW.

IT IS A BETRAYAL OF AMERICAN VALUES.

JOHN: KATHERINE YON EBRIGHT OF THE BRENNAN CENTER FOR JUSTICE.

THANK YOU VERY MUCH.

KATHERINE: THANK YOU.

JOHN: IN TODAY'S OTHER NEWS, THE DEATH TOLL FROM THE LINE OF MONSTER STORMS THAT SPAWNED TORNADOES, WILDFIRES AND DUST STORMS ROSE TO 35 PEOPLE TODAY.

THE FIERCE WEATHER MARCHED ACROSS THE CENTRAL AND SOUTHERN UNITED STATES, LEAVING A TRAIL OF DESTRUCTION.

COMMUNITIES IN MISSOURI AND ALABAMA WOKE UP TO WIDESPREAD DAMAGE, FLATTENED HOMES, CRUSHED CARS AND UPROOTED TREES.

IN WAYNE COUNTY, MISSOURI, DAKOTA HENDERSON HELPED SAVE HIS AUNT.

>> THE ONLY ROOM STANDING LEFT OF THIS HOUSE.

SHE WAS TRAPPED IN IT.

WE GOT HER OUT THE WINDOW, GOT HER UP TO THE EARTH HOME THAT'S UP THE ROAD.

AND WE, WE WERE HELPING OTHER PEOPLE.

WE FOUND A FEW BODIES THAT WAS OUT IN THE FIELD, A FEW DECEASED PEOPLE.

JOHN: THE STORM SYSTEM IS STILL POTENTIALLY DANGEROUS.

SEVERE WEATHER IS FORECAST FOR THE UPPER OHIO VALLEY, MID-ATLANTIC AND SOUTHEAST.

THE SYSTEM WON'T CLEAR THE EAST COAST UNTIL LATER TONIGHT.

IN NORTH MACEDONIA A MASSIVE FIRE THAT TORE THROUGH A NIGHTCLUB KILLED AT LEAST 59 PEOPLE AND INJURED 155 MORE.

IT HAPPENED EARLY THIS MORNING IN THE CITY OF KOCANI.

THE BLAZE APPEARED TO HAVE BEEN TOUCHED OFF BY SPARKLING PYROTECHNICS ON STAGE THAT WERE PART OF A BAND'S PERFORMANCE.

THROUGHOUT THE DAY TODAY, PEOPLE GATHERED OUTSIDE HOSPITALS TO AWAIT NEWS OF LOVED ONES.

MOST OF THE CONCERT-GOERS WERE YOUNG PEOPLE.

SO FAR, ARREST WARRANTS HAVE BEEN ISSUED FOR FOUR PEOPLE.

THE U.S. AND REBEL HOUTHIS IN YEMEN BOTH VOWED TO ESCALATE FIGHTING.

YESTERDAY, U.S.

FORCES LAUNCHED AIRSTRIKES ON THE IRANIAN BACKED GROUP IN AN EFFORT TO STOP THEM FROM TARGETING MILITARY AND COMMERCIAL SHIPS.

SECRETARY OF STATE MARCO RUBIO SAID THE HOUTHIS HAVE DIRECLTY ATTACKED THE U.S. NAVY 174 TIMES.

THE HOUTHI-RUN HEALTH MINISTRY CLAIMED THE U.S.

STRIKES KILLED 53 PEOPLE, AND SAID WOMEN AND CHILDREN WERE AMONG THE DEAD AND INJURED.

IRAN TODAY DENIED IT HAS ANY PART IN THE HOUTHIS ATTACKS IN THE RED SEA.

TWO NASA ASTRONAUTS ON THE INTERNATIONAL SPACE STATION GOT A WELCOME VISIT TODAY.

BUTCH WILMORE AND SUNI WILLIAMS OPENED THE HATCH AND GREETED THEIR REPLACEMENTS WITH HUGS AND HANDSHAKES.

THE FOUR NEWCOMERS ARE FROM THE UNITED STATES, JAPAN AND RUSSIA.

THEY'LL RELIEVE WILMORE AND WILLIAMS, WHO HAVE BEEN STUCK IN SPACE SINCE LAST JUNE.

THEIR BOEING STARLINER CAPSULE HAD SO MANY PROBLEMS THAT NASA INSISTED IT RETURN TO EARTH EMPTY.

STILL TO COME ON PBS NEWS WEEKEND, HOW CUTBACKS AT THE FAA COULD EFFECT AVIATION SAFETY.

AND A GLOBAL WARMING MILESTONE THAT HAS SCIENTISTS WORRIED.

JOHN: PRESIDENT TRUMP'S DRIVE TO SHRINK THE FEDERAL WORKFORCE HAS TOUCHED ABOUT EVERY AGENCY, INCLUDING THE FAA, WHICH IS RESPONSIBLE FOR AIR SAFETY.

IT COMES AT A TIME WHEN SAFETY IS GETTING A LOT OF ATTENTION BECAUSE OF RECENT INCIDENTS, INCLUDING JANUARY'S MID-AIR COLLISION OF A PASSENGER JET AND AN ARMY HELICOPTER.

AN ASSOCIATED PRESS NORC CENTER FOR PUBLIC AFFAIRS POLL LAST MONTH FOUND THAT 64% OF AMERICANS QUESTIONED SAID FLYING IS VERY SAFE OR SOMEWHAT SAFE.

THAT'S DOWN FROM 71% LAST YEAR.

ISAAC STANLEY BECKER IS A STAFF WRITER FOR THE ATLANTIC.

THE HEADLINE ON HIS STORY, LAST IN THE LAST ISSUE IS THE FAA'S TROUBLES ARE MORE SERIOUS THAN YOU KNOW.

ISAAC, WHAT IS THE SCALE OF THE LAYOFFS AT THE FAA?

HOW BIG ARE THEY?

ISAAC: THIS IS STILL TAKING SHAPE.

THE PRIMARY TWO WAYS THAT THE WORKFORCE IS BEING REDUCED IS THROUGH THE DISMISSAL OF PROBATIONARY EMPLOYEES.

AND THEN THIS OFFER OF EARLY RETIREMENT THAT WE SAW AT THE END OF JANUARY.

NOW, THERE ARE SOME LEGAL HANGUPS AROUND THE DISMISSAL OF THE PROBATIONARY EMPLOYEES, AND WE'RE SEEING THAT PLAY OUT IN THE COURTS, BUT IT COULD BE QUITE EXTENSIVE.

THAT IS WHAT MY REPORTING FOUND.

I WAS ABLE TO GET AHOLD OF SOME INTERNAL FAA DATA THAT SHOWED THAT MORE THAN 1300 PEOPLE AT THE AGENCY REPLIED TO THAT OFFER OF EARLY RETIREMENT, WITH MOST OF THEM QUITE INTERESTED IN TAKING IT.

AND THAT INCLUDED SOME PEOPLE IN QUITE CRITICAL SAFETY ROLES .

AVIATION SAFETY TECHNICIANS, QUALITY ASSURANCE SPECIALISTS, ENGINEERS AND PEOPLE WHO DO A LOT OF THE REALLY IMPORTANT BACKGROUND WORK THAT HELPS THOSE FRONTLINE SAFETY WORKERS DO THEIR JOBS CORRECTLY AND ACCURATELY.

JOHN: WE ASKED THE FAA ABOUT THE CUTS IN AVIATION SAFETY.

THEY SAID THE FAA CONTINUES TO HIRE AND ONBOARD AIR TRAFFIC CONTROLLERS AND SAFETY PROFESSIONALS, INCLUDING MECHANICS AND OTHERS WHO SUPPORT THEM.

THE AGENCY HAS RETAINED EMPLOYEES WHO PERFORM SAFETY CRITICAL FUNCTIONS.

BUT YOU'RE SAYING THAT SOME OF THE PEOPLE WHO WERE LAID OFF MAY NOT BE DIRECTLY INVOLVED WITH SAFETY, BUT THEY HAVE SORT OF TANGENTIAL CONNECTIONS TO IT?

ISAAC: WELL, WE SAW THE AGENCY MOVE TO EXEMPT FROM THAT BUYOUT PROGRAM AIR TRAFFIC CONTROLLERS, WHICH HAVE GOTTEN A LOT OF ATTENTION RECENTLY AFTER THAT TERRIBLE, TRAGIC INCIDENT AT REAGAN AIRPORT.

I SPOKE TO OFFICIALS INSIDE THE FAA, INCLUDING VERY SENIOR OFFICIALS, WHO SAID THAT THERE WERE STILL CRITICAL SAFETY FUNCTIONS THAT SUPPORT THOSE FRONT LINE SAFETY STAFF THAT WERE BEING SACRIFICED.

JUST TO GIVE ONE EXAMPLE, AERONAUTICAL INFORMATION SPECIALISTS.

THESE ARE THE PEOPLE WHO UPDATE THE CHARTS AND THE MAPS AND THE KEY DATA AFTER THERE ARE DISRUPTIONS OR DISTURBANCES IN AIRSPACE, WEATHER, NATURAL DISASTERS, A COLLISION AND ACCIDENT INVESTIGATION.

AND WHAT I FOUND IS THAT THROUGH THE COMBINATION OF THAT BUYOUT PROGRAM AND THE DISMISSAL, PROBATIONARY EMPLOYEES, ABOUT 12% OF THOSE PEOPLE ARE HAVE EITHER LEFT AGENCY OR ARE POISED TO LEAVE THE AGENCY.

AND THAT'S A REALLY IMPORTANT ROLE.

SO IT'S ENCOURAGING THAT THE FAA IS TAKING STEPS TO RETAIN AIR TRAFFIC CONTROLLERS AND EVEN DO SOME ADDITIONAL HIRING BUT I THINK IT'S WORTH CONSIDERING SOME OF THE OTHER LESS WELL RECOGNIZED ROLES THAT ARE BEING SACRIFICED AMID ALL OF THIS.

JOHN: HOW CONCERNED ARE THE PEOPLE YOU TALK WITHIN THE AGENCY ABOUT THOSE LAYOFFS?

ISAAC: WHAT I'LL SAY IS THIS I THINK THAT THEY ARE CONCERNED.

THEY ALSO STRESS THE REDUNDANCIES AND RESILIENCIES BUILT INTO THE SYSTEM, AND EMPHASIZED THAT THESE ARE ABSOLUTE PROFESSIONALS WHO ARE IN CHARGE OF ENSURING THE SAFETY OF THIS SYSTEM THAT MILLIONS OF PASSENGERS RELY ON EVERY DAY TO MOVE SAFELY AROUND THE COUNTRY.

I THINK IT WOULD BEHOOVE THE AGENCY, THOUGH, TO SAY MORE ABOUT WHAT IT'S DOING TO REASSURE THE WORKFORCE, TO FILL SOME OF THESE CRITICAL POSITIONS AND TO ENSURE THAT OUR AVIATION SAFETY SYSTEM REMAINS THE GOLD STANDARD.

JOHN: THE MAIN FIGURE IN ALL THIS WORKFORCE REDUCTION IS, OF COURSE, ELON MUSK.

HIS STARLINK HAS OFFERED TO UPGRADE THE FAA'S COMMUNICATION SYSTEM, WHICH IS OUTDATED, AND THIS HAS BEEN A LONG, ONGOING STORY FOR THEM.

THEY'VE STARTED TESTING, AND YOU'VE WRITTEN THAT THERE ARE SOME CONCERNS ABOUT THAT.

ISAAC: THERE ARE.

AND YOU MAKE SUCH A CRITICAL POINT ABOUT THE SYSTEM BEING OUTDATED AND THIS BEING A LONG TIME CONCERN.

IT'S A SYSTEM THAT DATES TO 2002.

IT STILL USES COPPER WIRING, OTHER KINDS OF OUTDATED SYSTEMS, AND THE AGENCY HAS BEEN AWARE OF THIS.

IN 2023, THEY AWARDED A $2.4 BILLION CONTRACT TO VERIZON TO UPGRADE THE SYSTEM.

WHAT MUSK WANTS TO DO IS DEPLOY THOUSANDS OF STARLINK TERMINALS FROM HIS PRIVATE COMPANY, SPACEX, AROUND THE COUNTRY TO SUPPORT THE AGENCY'S COMMUNICATIONS INFRASTRUCTURE.

AND I THINK THE CONCERNS ARE REALLY TWOFOLD.

ONE IS ABOUT POTENTIAL CONFLICTS OF INTEREST.

THIS IS SOMEONE WHO HAS AN INTEREST IN THE COMMERCIAL SUCCESS OF THIS COMPANY.

AND ALSO IT'S A COMPANY THAT IS A REGULATED ENTITY BEFORE OTHER DIVISIONS OF THE FAA AND THEN ALSO SOME SECURITY, SOME CYBERSECURITY CONCERNS.

I SPOKE TO EXPERTS WHO PARTICIPATED IN A CONFIDENTIAL TASK FORCE LAST YEAR AROUND CYBERSECURITY FOR THE FAA.

AND THEY SAID THERE'S A REASON WHY CONTRACTORS LIKE VERIZON ARE USED, AND IT'S BECAUSE THEY'VE GONE THROUGH A VERY RIGOROUS SECURITY AND COMPLIANCE PROCESS, KNOWN AS FEDRAMP, TO ENSURE CYBERSECURITY STANDARDS, THREAT PREVENTION AND SO ON AND SO FORTH.

AND STARLINK AND SPACEX HAVE NOT DONE THAT.

JOHN: YOU MENTIONED SPACEX, WHICH ALSO IS REGULATED AS, AS YOU SAY, BY THE FAA LAST FALL, THE FAA MOVED TO FINE SPACEX OVER SOME LICENSING ISSUES.

AND ELON MUSK REFERRED TO IT CALLED IT LAWFARE.

ARE THEIR CONCERNS ABOUT THAT, THAT HE HAS INTEREST BEFORE THE FAA?

ISAAC: THERE ARE CONCERNS.

AND I THINK THAT A NUMBER OF THESE PEOPLE, THERE ARE PEOPLE WHO THINK IN TERMS OF THE WORST CASE.

SO WHAT THEIR CONCERN IS, AND THE WORST CASE IS THAT YOU'RE MAKING THE COMMUNICATIONS NETWORK OF THIS CRITICAL AGENCY DEPENDENT ON THIS BILLIONAIRE TRUMP ALLY.

AND WHAT IF YOU WERE TO SET TO - - WHAT IF YOU WERE TO DECIDE TO GO IN A DIFFERENT DIRECTION OR DO SOMETHING DRASTIC?

WE'VE SEEN HOW THESE STARLINK TERMINALS ARE USED IN UKRAINE, AND ITS CONFLICT WITH RUSSIA.

AND THERE WAS AN INSTANCE IN 2022 WHEN MUSK DECIDED TO SHUT SOME OF THOSE TERMINALS OFF BECAUSE HE DIDN'T WANT THEM USED AS PART OF AN OFFENSIVE RAID AGAINST RUSSIA.

AND THIS FACED A LOT OF CRITICISM AT THE TIME.

BUT THE E NCERN AGAIN IS WHAT IF BECAUSE OF AN N VERSE ACTION BY THE FAA, HE WERE TO BE SO ENRAGED BY THIS THAT HE WOULD TRY TO USE THE TERMINALS USED AS PART OF THE COMMUNICATIONS INFRASTRUCTURE AS LEVERAGE?

AND THAT WOULD, I THINK, BE A KIND OF WORST CASE FOR THE AGENCY.

JOHN: ISAAC STANLEY BECKER OF THE ATLANTIC, THANK YOU VERY MUCH.

ISAAC: THANK YOU.

JOHN: THIS PAST WEEK, THE EPA SAID IT IS RECONSIDERING THE SCIENTIFIC FINDING THAT GREENHOUSE GASES ARE A DANGER TO PUBLIC HEALTH, A FINDING THAT'S BEEN AT THE CENTER OF THIS COUNTRY'S FIGHT AGAINST CLIMATE CHANGE.

THIS COMES AS RESEARCH SHOWS AVERAGE GLOBAL TEMPERATURES IN 2024 LIKELY ROSE ABOVE A 1.5 DEGREE CELSIUS THRESHOLD THAT R YEARS HAS BEEN AN ENVIRONMENTAL RED LINE.

ALI ROGIN SPOKE WITH MICHAEL MANN, THE DIRECTOR OF THE CENTER FOR SCIENCE, SUSTAINABILITY AND THE MEDIA AT THE UNIVERSITY OF PENNSYLVANIA.

ALI: MICHAEL, THANK YOU SO MUCH FOR BEING HERE.

SIMPLY PUT, HOW BIG A DEAL IS IT FOR THE PLANET TO EXCEED THIS 1.5 DEGREE THRESHOLD?

MICHAEL: WELL, IT'S A BIG DEAL, BUT IT SHOULD BE PUT IN CONTEXT.

WHAT HAPPENED THIS YEAR WAS THAT WE HAD AN EL NINO EVENT.

IT'S A NATURAL WARMING EVENT THAT ADDS TO THE GLOBAL TEMPERATURE.

SO IT BOOSTED IT TEMPORARILY ABOVE THAT 1.5 CELSIUS MARK.

WHAT WE'RE REALLY CONCERNED ABOUT IS WHEN THE TREND LINE ITSELF CROSSES 1.5 CELSIUS, ROUGHLY THREE DEGREES FAHRENHEIT, AND THAT WILL PROBABLY HAPPEN IN LITTLE MORE THAN A DECADE IF WE CONTINUE ON THIS CURRENT COURSE.

AND SO I SORT OF LIKEN IT TO, IF YOU GET A 50 DEGREE OR 60 DEGREE DAY IN LATE FEBRUARY, IT DOESN'T MEAN WINTER IS OVER, BUT IT'S AN INDICATION THAT THE END OF WINTER IS PROBABLY COMING.

THIS IS AN INDICATION THAT WE'RE GETTING PERILOUSLY CLOSE TO THIS VERY DANGEROUS THRESHOLD.

ALI: AND WHAT HAPPENS IF WE DO CONTINUE TO EXCEED THIS NUMBER?

THAT'LL BE A SIGN THAT THINGS ARE CONTINUING TO MOVE IN THAT DIRECTION IN A IN A MORE PERMANENT WAY RIGHT?

MICHAEL: YEAH.

AND SO, YOU KNOW, IT'S NOT LIKE A CLIFF THAT WE GO OFF AT THAT LEVEL OF WARMING.

IT'S MORE LIKE A DANGEROUS HIGHWAY THAT WE'RE GOING DOWN.

EVERY BIT OF ADDITIONAL WARMING MAKES THINGS WORSE, BUT CONVERSELY, EVERY BIT OF WARMING THAT WE CAN PREVENT MAKES THINGS BETTER.

AND SO IT'S IMPORTANT FOR US TO, YOU KNOW, GET OFF THE BURNING OF FOSSIL FUELS AS QUICKLY AS WE CAN, LIMIT WARMING AS MUCH AS WE CAN.

AND THIS IS JUST AN INDICATION THAT WE ARE, YOU KNOW, HEADED TOWARDS EVER MORE DANGEROUS LEVELS OF CLIMATE CHANGE.

ALI: AND WHAT IS IT ABOUT THAT 1.5 DEGREE CHANGE?

I'VE READ THAT IT'S NOT SO MUCH THAT NUMBER ITSELF, IT'S THAT IT'S MORE ABOUT WHAT IT REPRESENTS.

IS THAT CORRECT?

MICHAEL: IT IS, BECAUSE IT'S A CONTINUOUS SCALE.

AND, YOU KNOW, THE DEVASTATING WILDFIRES WE'VE SEEN OUT WEST, THE HURRICANE SEASON, THE TREMENDOUS FLOODING THAT WE SAW IN PARTS OF THE SOUTHEASTERN U.S.

THE MORTALITY THAT CAME WITH THAT.

THIS IS AN INDICATION THAT WE ARE ALREADY SEEING TRULY DANGEROUS CLIMATE CONSEQUENCES AND THEY WILL JUST GET MORE AND MORE DANGEROUS.

WE WILL SEE MORE FREQUENT AND MORE INTENSE WEATHER EXTREMES OF THE SORT THAT WE'VE SEEN IF WE CONTINUE DOWN THIS ROAD.

AND SO WE NEED TO, YOU KNOW, REDUCE OUR CARBON EMISSIONS AS QUICKLY AS POSSIBLE TO PREVENT THINGS FROM GETTING EVEN WORSE.

ALI: PRESIDENT TRUMP HAS STARTED THE PROCESS OF WITHDRAWING FROM THE PARIS CLIMATE AGREEMENT, WHICH SET THIS 1.5 DEGREE THRESHOLD, ALSO EASING RESTRICTIONS ON OIL AND GAS PRODUCTION.

HOW DOES THAT IMPACT EFFORTS TO AVOID FURTHER EXCEEDING THIS THRESHOLD?

AND WHAT ABOUT THE GENERAL POLITICAL CLIMATE ELSEWHERE IN THE WORLD?

MICHAEL: THE REAL PROBLEM HERE IS THAT THIS SORT OF SENDS A SIGNAL TO THE REST OF THE WORLD THAT THE UNITED STATES ISN'T WILLING TO HONOR ITS COMMITMENTS.

WE'RE THE WORLD'S LARGEST LEGACY CARBON POLLUTER.

WE'VE PUT MORE CARBON POLLUTION INTO THE ATMOSPHERE THAN ANY OTHER COUNTRY, AND THAT'S ALL THE CLIMATE CARES ABOUT.

IT CARES ABOUT THE CUMULATIVE CARBON EMISSIONS.

OVER TIME, WE'VE CONTRIBUTED MORE TO THE WARMING OF THE PLANET THAN ANY OTHER COUNTRY.

FORTUNATELY, WE HAVE SEEN SOME DEGREE OF RESOLVE.

THE EU REMAINS COMMITTED.

CHINA SEEMS TO BE STEPPING UP.

I THINK THEY SEE AN OPPORTUNITY FOR ACTUALLY TAKING LEADERSHIP IN THE VACUUM LEFT BY U.S. DISENGAGEMENT UNDER THE NEW TRUMP ADMINISTRATION.

SO IT'S A GLOBAL PROBLEM.

IT REQUIRES GLOBAL COOPERATION.

AND SO WE WILL HAVE TO SEE WHAT OTHER COUNTRIES DO.

ALI: AND IN TERMS OF THAT GLOBAL PARTICIPATION, THERE'S LONG BEEN A DEBATE ABOUT THE RESPONSIBILITY OF DEVELOPING COUNTRIES AND WHAT THEY HAVE TO DO VERSUS DEVELOPED FIRST WORLD COUNTRIES LIKE THE UNITED STATES.

HOW DOES THE REACHING AND EXCEEDING OF THIS 1.5 DEGREE THRESHOLD MOVE THE NEEDLE ON THAT DEBATE?

MICHAEL: YOU KNOW, THE COMBINATION OF THE FACT THAT WE'RE GETTING PERILOUSLY CLOSE TO THIS NEW DANGEROUS MILESTONE AND THE FACT THAT THIS IS HAPPENING IN AN ERA OF U.S. DISENGAGEMENT.

IT DOES PROVIDE AN EXCUSE TO DEVELOPING COUNTRIES WHO CAN RIGHTLY SAY, LOOK, YOU HAD ACCESS TO TWO CENTURIES OF CHEAP, DIRTY FOSSIL FUEL ENERGY TO GROW YOUR ECONOMY.

AND IF YOU'RE NOT WILLING TO DO SOMETHING TO HELP THE WORLD DEAL WITH THIS PROBLEM, THEN WHY SHOULDN'T WE GET OUR OWN OPPORTUNITY TO GROW OUR ECONOMIES?

MANY OF THESE DEVELOPING COUNTRIES HAVE CONTRIBUTED THE LEAST TO THE PROBLEM, AND THEY'RE ALREADY BEARING THE BRUNT OF THE PROBLEM.

THEY'RE SEEING SOME OF THE WORST CONSEQUENCES.

THEY HAVE THE LEAST WEALTH AND RESILIENCE TO DEAL WITH THE CONSEQUENCES THAT ARE ALREADY HAPPENING.

WE HAVE TO PROVIDE SOME DEGREE OF ASSISTANCE TO DEVELOPING COUNTRIES TO HELP THEM DEAL WITH THE CATASTROPHIC CONSEQUENCES THEY'RE ALREADY DEALING WITH AND TO HELP THEM SORT OF LEAPFROG PAST THE DIRTY FOSSIL FUEL STAGE OF ECONOMIC DEVELOPMENT.

WE WANT TO SEE THEM BYPASSED, - - WE WANT TO SEE THEM BYPASSED THAT -- BYPASS THAT.

WE CAN'T AFFORD THEM TO MAKE THE SAME MISTAKES THAT WE MADE, AND WE HAVE TO MAKE IT WORTH THEIR WHILE TO MOVE DIRECTLY TO CLEAN, RENEWABLE ENERGY SOURCES.

ALI: MICHAEL MANN, DIRECTOR OF THE CENTER FOR SCIENCE, SUSTAINABILITY AND THE MEDIA AT THE UNIVERSITY OF PENNSYLVANIA.

THANK YOU SO MUCH FOR JOINING US.

MICHAEL: THANK YOU.

JOHN: AND THAT IS PBS NEWS WEEKEND FOR THIS SUNDAY.

I'M JOHN YANG.

FOR ALL OF MY COLLEAGUES, THANKS FOR JOINING US.

HAVE A GOOD WEEK.