REU opportunities by topic: https://www.nsf.gov/crssprgm/reu/reu_search.jsp Deadlines vary; usually winter
NSF Graduate Research Fellowship Program (GRFP): https://www.nsfgrfp.org/ Deadlines every fall
Ford Foundation fellowships (via National Academy of Sciences) for underrepresented students (predoctoral, doctoral postgraduate): https://www.nationalacademies.org/our-work/ford-foundation-fellowships
NCAR/UCAR undergraduate Internship opportunities: https://ncar.ucar.edu/opportunities/internships and https://soars.ucar.edu
Georgia Tech Broadening Participation in Atmospheric Science, Oceanography, and Geosciences REU Program: https://easreu.eas.gatech.edu/ Deadline in January or February
Georgia Tech Aquatic Chemical Ecology REU Program: https://reu.biosciences.gatech.edu/ Deadline in February or March
AGU Bridge Program: offers the opportunity to apply for a PhD at many Universities to underrepresented students. University partners guarantee two years of support by being part of the Program (lot of flexibility for selected students): https://www.agu.org/learn-and-develop/learn/travel-research-grants/agu-bridge-program
ACS Bridge Program: similar to AGU Bridge but in Chemistry: https://www.acs.org/education/students/graduate/bridge-project/students.html
Many more fellowship opportunities through federal agencies and private foundations can be found at https://eas.gatech.edu/graduate/fellowship-opportunities
The Direct Air Capture Center at GT (opportunities for research and collaborations)